Steam reforming heated by resistance heating

ABSTRACT

A reactor system for carrying out steam reforming of a feed gas comprising hydrocarbons, including: a structured catalyst arranged for catalyzing steam reforming of a feed gas including hydrocarbons, the structured catalyst including a macroscopic structure of electrically conductive material, the macroscopic structure supporting a ceramic coating, wherein the ceramic coating supports a catalytically active material; a pressure shell housing the structured catalyst; heat insulation layer between the structured catalyst and the pressure shell; at least two conductors electrically connected to the macroscopic structure and to an electrical power supply placed outside the pressure shell, wherein the electrical power supply is dimensioned to heat at least part of the structured catalyst to a temperature of at least 500° C. by passing an electrical current through the macroscopic structure. Also, a process for steam reforming of a feed gas comprising hydrocarbons.

FIELD OF THE INVENTION

Embodiments of the invention relate to a reactor system and a processfor carrying out steam reforming of a feed gas comprising hydrocarbonswhere the heat for the endothermic reaction is provided by resistanceheating.

BACKGROUND

Steam reforming reactions will often be challenged by how efficient heatcan be transferred to the reactive zone of the catalyst bed within areactor unit. Conventional heat transfer by convection, conduction,and/or radiation heating can be slow and will often meet largeresistance in many configurations. This challenge can be illustratedwith the tubular reformer in a steam reforming plant, which practicallycan be considered as a large heat exchanger with heat transfer as therate limiting step. The temperature at the innermost part of the tubesof the tubular reformer is somewhat lower than the temperature outsidethe tubes due to the heat transfer rate through the walls of the tubeand to the catalyst within the tubes as well as due to the endothermicnature of the steam reforming reaction.

One way to supply heat within catalyst instead of outside the tubeshousing the catalyst is by means of electrical resistance heating.DE102013226126 describes a process for allothermal methane reformingwith physical energy reclamation, wherein methane is reformed by meansof carbon dioxide to synthesis gas consisting of carbon monoxide andhydrogen. The starting gases CH₄ and CO₂ are conducted in a fixed bedreactor consisting of electrically conductive and catalytic particles,which is electrically heated to temperatures of about 1000 K. Theconversion of the reactant gases and the generation of heat of thegenerated synthesis gas take place in the fixed bed reactor.

It is an object of the invention to provide an alternative configurationof an electrically heated reactor system for carrying out steamreforming.

It is also an object of the invention to provide a reactor system withintegrated heat supply and catalysts.

It is a further object of the invention to provide a reactor system andprocess for producing synthesis gas by steam reforming wherein theoverall energy consumption is reduced compared to a system with anexternally heated reactor, such as a side fired or top fired steammethane reformer (SMR), which is the reference for industrial scalesteam reforming. By utilizing electric heating, the high temperatureflue gas of the fired SMR is avoided and less energy is therefore neededin the reforming section of the electrically heated reactor.

It is another object of the invention to provide a reactor system andprocess for producing synthesis gas by steam reforming wherein theamount of catalyst and the size of the reactor system is reducedcompared to an SMR. Moreover, the invention provides for the possibilityof tailoring and thus reducing the amount of catalytically activematerial, while having a controlled reaction front of the reformingreaction.

It is also an object of the invention to provide a reactor system andprocess for producing synthesis gas by steam reforming where the amountof synthesis gas produced in a single pressure shell is increasedconsiderably compared to known tubular steam reformers.

It is furthermore an object of the invention to provide a process forproduction of a synthesis gas by use of a steam reforming reactorsystem, wherein the synthesis gas output from the steam reformingreactor system has a relatively high temperature and a relatively highpressure. In particular, it is desirable if the temperature of thesynthesis gas output from the steam reforming reactor system is betweenabout 900° C. and 1100° C. or even up to 1300° C., and if the pressureof the synthesis gas output from the steam reforming reactor system isbetween about 30 bar and about 100 bar. The invention will allow forprecise control of the temperature of the synthesis gas output from thesteam reforming reactor system.

An advantage of the invention is that the overall emission of carbondioxide and other emissions detrimental to the climate may be reducedconsiderably, in particular if the power used in the reactor system isfrom renewable energy resources.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to a reactor system forcarrying out steam reforming of a feed gas comprising hydrocarbons, thereactor system comprising:

-   -   a structured catalyst arranged for catalyzing steam reforming of        a feed gas comprising hydrocarbons, the structured catalyst        comprising a macroscopic structure of electrically conductive        material, the macroscopic structure supporting a ceramic        coating, wherein the ceramic coating supports a catalytically        active material, where the pressure shell comprises an inlet for        letting in the feed gas and an outlet for letting out product        gas, wherein the inlet is positioned so that the feed gas enters        the structured catalyst in a first end of the structured        catalyst and the product gas exits the structured catalyst from        a second end of the structured catalyst;    -   a pressure shell housing the structured catalyst;    -   heat insulation layer between the structured catalyst and the        pressure shell;    -   at least two conductors electrically connected to the structured        catalyst and to an electrical power supply positioned outside        the pressure shell, wherein the electrical power supply is        dimensioned to heat at least part of the structured catalyst to        a temperature of at least 500° C. by passing an electrical        current through the structured catalyst, wherein the at least        two conductors are connected to the structured catalyst at a        position on the structured catalyst closer to the first end of        the structured catalyst than to the second end of the structured        catalyst, and wherein the structured catalyst is constructed to        direct an electrical current to run from one conductor        substantially to the second end of the structured catalyst and        return to a second of the at least two conductors.

The layout of the reactor system allows for feeding a pressurized feedgas to the reactor system at an inlet and directing this gas into thepressure shell of the reactor system. Inside the pressure shell, aconfiguration of heat insulation layers and inert material is arrangedto direct the feed gas through the channels of the structured catalystwhere it will be in contact with the ceramic coating and thecatalytically active material supported on the ceramic coatings, wherethe catalytically active material will facilitate the steam reformingreaction. Additionally, the heating of the structured catalyst willsupply the required heat for the endothermic reaction. The product gasfrom the structured catalyst is led to the reactor system outlet.

The term “first end of the structured catalyst” is meant to denote theend of the structured catalyst where the feed gas enters the structuredcatalyst, and the term “second end of the structured catalyst” is meantto denote the end of the structured catalyst from which the gas exitsthe structured catalyst. Moreover, it should be noted that the term “theat least two conductors are connected to the structured catalyst at aposition on the structured catalyst closer to the first end of thestructured catalyst than to the second end of the structured catalyst”is meant to denote that both/all of the at least two conductors areconnected closer to the first end of the structured catalyst than to thesecond end. Preferably, the at least two conductors are connected tofirst end of the structured catalyst or within the quarter of the lengthof the/a macroscopic structure closest to the first end.

The close proximity between the catalytically active material and themacroscopic structures enables efficient heating of the catalyticallyactive material by solid material heat conduction from the resistanceheated macroscopic structure. An important feature of the resistanceheating process is thus that the energy is supplied inside the objectitself, instead of being supplied from an external heat source via heatconduction, convection and radiation. Moreover, the hottest part of thereactor system will be within the pressure shell of the reactor system.Preferably, the electrical power supply and the structured catalyst aredimensioned so that at least part of the structured catalyst reaches atemperature of 850° C., preferably 900° C., more preferably 1000° C. oreven more preferably 1100° C. The amount and composition of thecatalytically active material can be tailored to the steam reformingreaction at the given operating conditions. The surface area of themacroscopic structure, the fraction of the macroscopic structure coatedwith a ceramic coating, the type and structure of the ceramic coating,and the amount and composition of the catalytically active catalystmaterial may be tailored to the steam reforming reaction at the givenoperating conditions. However, it should be noted, that advantageouslysubstantially all the surface of the macroscopic structure is coatedwith the ceramic coating and preferably all or most of the ceramiccoating supports the catalytically active material. Preferably, only theparts of the macroscopic coating which are connected to conductors, arenot provided with the ceramic coating. The ceramic coating supportingthe catalytically active material reduces or prevents the risk of carbonformation according to the reaction:

CH₄⇄C+2H₂  (A)

The coverage of the metallic structure with the ceramic coatingsupporting the catalytically active material ensures that the metallicphase of the macroscopic structure is covered by a coherent oxide layerwhich has less potential for carbon forming reactions. Furthermore, thecatalytically active material of the oxide phase will catalyze the steamreforming reactions and bring the reactant gas towards, or even closeto, thermodynamic equilibrium. This increases the partial pressure ofhydrogen and decreases the partial pressure of methane thereby reducingor in many cases eliminating the thermodynamic potential for carbonformation according to reaction (A) above.

When the pressure shell comprises an inlet for letting in process gasand an outlet for letting out product gas, where the inlet is positionedso that the feed gas enters the structured catalyst in a first end ofthe structured catalyst and the product gas exits the structuredcatalyst from a second end of the structured catalyst, and when the atleast two conductors both are connected to the structured catalyst at aposition on the structured catalyst closer to the inlet than to theoutlet, the at least two conductors can be placed in the relativelycolder part of the reactor system. The first end of the structuredcatalyst has a lower temperature than the second end of the structuredcatalyst due to:

-   -   the feed gas fed led through the inlet may cool the at least two        conductors before being heated by the structured catalyst        further along the path of the gas through the structured        catalyst;    -   the feed gas inlet into the first end of the structured catalyst        will have lower temperature than the product gas leaving the        second end of the structured catalyst, due to the heat supplied        to the structured catalyst electrically,    -   The endothermic nature of the steam reforming reaction absorbs        heat,    -   The structured catalyst is constructed to direct an electrical        current to run from one conductor substantially to the second        end of the structured catalyst and return to a second of the at        least two conductors.

Therefore, the temperature profile in of the structured catalyst willcorrespond to a substantially continuously increasing temperature alongthe path of the feed gas through the structured catalyst. Thiscorresponds to a substantially increasing conversion rate of methane inthe feed gas to hydrogen and carbon monoxide.

Hereby, the current is led into the macroscopic structure and out fromthe macroscopic structure through conductors positioned in therelatively cold first end thereof. It is an advantage that thetemperature of all electrically conducting elements except themacroscopic structure is kept down in order to protect the connectionsbetween the conductors and the structured catalyst. When the temperatureof the conductors and other electrically conducting elements, except themacroscopic structure, is relatively low, less limitations on materialssuitable for the conductors and other electrically conducting elements,except the macroscopic structure, exists. When the temperature of theelectrically conducting elements increase, the resistivity thereofincreases; therefore, it is desirable to avoid unnecessary heating ofall other parts than the macroscopic structures within the reactorsystem.

Moreover, the combination of heat insulation and connection of theconductors to the first colder end of the macroscopic structure rendersit possible to increase the pressure of the pressure shell to more than5 bar.

It should be noted that the term “electrically conducting elements,except the macroscopic structure” is meant to cover the relevantelectrically conducting elements arranged to connect the power supply tothe structured catalyst and potential connections in between macroscopicstructures or structured catalysts.

The combination of the substantially continuously increasing temperatureprofile of the structured catalyst along the path of the feed gasthrough the structured catalyst and a controllable heat flux from thestructured catalyst, control of the reaction front of the chemicalreaction is achievable.

As used herein, the term “macroscopic structure” is meant to denote astructure which is large enough to be visible with the naked eye,without magnifying devices. The dimensions of the macroscopic structureare typically in the range of tens of centimeters or of meters.Dimensions of the macroscopic structure are advantageously made tocorrespond at least partly to the inner dimensions of the pressure shellhousing the structured catalyst, saving room for the heat insulationlayer and conductors. Two or more macroscopic structures may beconnected in order to provide an array of macroscopic structures havingat least one of the outer dimensions in the range of meters, such as 0.5m, 1 m, 2 m or 5 m. Such two or more macroscopic structures may bedenoted “an array of macroscopic structures”. In this case thedimensions of an array of macroscopic structures are advantageously madeto correspond at least partly to the inner dimension of the pressureshell housing the structured catalyst (saving room for the heatinsulation layer). A conceivable array of macroscopic structures couldtake up a volume of 0.1 to 10 m³ or even larger. A “structured catalyst”may comprise a single macroscopic structure or an array of macroscopicstructures, where the macroscopic structure(s) support(s) a ceramiccoating supporting catalytically active material. If the structuredcatalyst comprises an array of macroscopic structures, the macroscopicstructures may be electrically connected to each other; however,alternatively, the macroscopic structures are not electrically connectedto each other. Thus, the structured catalyst may comprise two or moremacroscopic structures positioned adjacent to each other. Themacroscopic structure(s) may be extruded and sintered structures. Themacroscopic structure(s) may alternatively be 3D printed and sintered.

The physical dimensions of the macroscopic structure may be anyappropriate dimensions; thus, the height may be smaller than the widthof the macroscopic structure or vice versa.

The macroscopic structure supports a ceramic coating, where the ceramiccoating supports a catalytically active material. The term “macroscopicstructure supporting a ceramic coating” is meant to denote that themacroscopic structure is coated by the ceramic coating at, at least, apart of the surface of the macroscopic structure. Thus, the term doesnot imply that all the surface of the macroscopic structure is coated bythe ceramic coating; in particular, at least the parts of themacroscopic structure which are electrically connected to the conductorsdo not have a coating thereon. The coating is a ceramic material withpores in the structure which allows for supporting catalytically activematerial on and inside the coating. Advantageously, the catalyticallyactive material comprises catalytically active particles having a sizein the range from about 5 nm to about 250 nm.

Preferably, the macroscopic structure has been manufactured by extrusionof a mixture of powdered metallic particles and a binder to an extrudedstructure and subsequent sintering of the extruded structure, therebyproviding a material with a high geometric surface area per volume.Alternatively, the macroscopic structured has been 3D printed.Preferably, the extruded or 3D printed structure is sintered in areducing atmosphere to provide the macroscopic structure. A ceramiccoating, which may contain the catalytically active material, isprovided onto the macroscopic structure before a second sintering in anoxidizing atmosphere, in order to form chemical bonds between theceramic coating and the macroscopic structure. Alternatively, thecatalytically active material may be impregnated onto the ceramiccoating after the second sintering. When chemical bonds are formedbetween the ceramic coating and the macroscopic structure an especiallyhigh heat conductivity between the electrically heated macroscopicstructure and the catalytically active material supported by the ceramiccoating is possible, offering close and nearly direct contact betweenthe heat source and the catalytically active material of the structuredcatalyst. Due to close proximity between the heat source and thecatalytically active material the heat transfer is effective, so thatthe structured catalyst can be very efficiently heated. A compactreactor system in terms of gas processing per reactor system volume isthus possible, and therefore the reactor system housing the structuredcatalyst may be compact.

As used herein, the terms “3D print” and “3D printing” is meant todenote a metal additive manufacturing process. Such metal additivemanufacturing processes cover 3D printing processes in which material isjoined to a structure under computer control to create athree-dimensional object, where the structure is to be solidified, e.g.by sintering, to provide the macroscopic structure. Moreover, such metaladditive manufacturing processes cover 3D printing processes which donot require subsequent sintering, such as powder bed fusion or directenergy deposition processes. Examples of such powder bed fusion ordirect energy deposition processes are laser beam, electron beam orplasma 3D printing processes.

The reactor system of the invention does not need a furnace and thisreduces the overall reactor size considerably. Moreover, it is anadvantage that the amount of synthesis gas produced in a single pressureshell is increased considerably compared to known tubular steamreformers. In a standard tubular steam reformer, the amount of synthesisgas produced in a single tube of the tubular steam reformer is up to 500Nm³/h. In comparison, the reactor system of the invention is arranged toproduce up to or more than 2000 Nm³/h, e.g. even up to or more than10000 Nm³/h, within a single pressure shell. This can be done withoutthe presence of O₂ in the feed gas and with less than 10% methane in thesynthesis gas produced. When a single pressure shell houses catalyst forproducing up to 10000 Nm³/h synthesis gas, it is no longer necessary toprovide a plurality of pressure shells or means for distributing feedgas to a plurality of such separate pressure shells.

Another advantage of the reactor system is that the flow through thestructured catalyst within the reactor system may be upflow, due to thestructured catalyst comprising a macroscopic structure. Alternatively,the flow through the structured catalyst could be in the horizontaldirection or any other appropriate direction. This is more difficult inthe case where the reactor contains pellets due to the risk offluidization, grinding, and blowing out the pellets. Thereby, asubstantial amount of piping may be avoided, thus reducing plant costs.Furthermore, the possibility of upflow or horizontal flow increases theflexibility in plant design.

Preferably, the macroscopic structure comprises Fe, Cr, Al, or an alloythereof. Such an alloy may comprise further elements, such as Si, Mn, Y,Zr, C, Co or combinations thereof. The catalytically active material maye.g. comprise nickel, ruthenium, rhodium, iridium, platinum, cobalt, ora combination thereof. Thus, one possible catalytically active materialis a combination of nickel and rhodium and another combination of nickeland iridium. The ceramic coating may for example be an oxide comprisingAl, Zr, Mg, Ce and/or Ca. Exemplary coatings are calcium aluminate or amagnesium aluminum spinel. Such a ceramic coating may comprise furtherelements, such as La, Y, Ti, K, or combinations thereof. Preferably, theconductors and the macroscopic structure are made of different materialsthan the macroscopic structure. The conductors may for example be ofiron, nickel, aluminum, copper, silver, or an alloy thereof. The ceramiccoating is an electrically insulating material and will typically have athickness in the range of around 100 μm, e.g. about 10-500 μm.

The macroscopic structure is advantageously a coherent or consistentlyintra-connected material in order to achieve electrical conductivitythroughout the macroscopic structure, and thereby achieve thermalconductivity throughout the structured catalyst and in particularproviding heating of the a catalytically active material supported bythe macroscopic structure. By the coherent or consistentlyintra-connected material it is possible to ensure uniform distributionof current within the macroscopic structure and thus uniformdistribution of heat within the structured catalyst. Throughout thistext, the term “coherent” is meant to be synonymous to cohesive and thusrefer to a material that is consistently intra-connected or consistentlycoupled. The effect of the structured catalyst being a coherent orconsistently intra-connected material is that a control over theconnectivity within the material of the structured catalyst and thus theconductivity of the macroscopic structure is obtained. It is to be notedthat even if further modifications of the macroscopic structure arecarried out, such as provision of slits within parts of the macroscopicstructure or the implementation of insulating material within themacroscopic structure, the macroscopic structure is still denoted acoherent or consistently intra-connected material.

As shown in the figures, the gas flow through the structured catalyst isaxial or co-axial with the length or z-axis of the structured catalyst.Even though the figures show that the z-axis of the structured catalystis vertical, it should be noted that the reactor can be positioned inany suitable way, so that the structured catalyst and the gas flowthrough it can e.g. be horizontal, upside down compared to the figures,or angled at e.g in 45° to horizontal.

In this context, the term “hydrocarbon gas” is meant to denote a gaswith one or more hydrocarbons and possibly other constituents. Thus,typically the hydrocarbon gas comprises CH₄ and optionally also higherhydrocarbons in relatively small amounts in addition to small amounts ofother gasses. Higher hydrocarbons are components with two or more carbonatoms such as ethane and propane. Examples of “hydrocarbon gas” may benatural gas, town gas, naphtha or a mixture of methane and higherhydrocarbons. Hydrocarbons may also be components with other atoms thancarbon and hydrogen such as oxygenates. The term “feed gas comprisinghydrocarbons” is meant to denote a feed gas comprising a hydrocarbon gaswith one or more hydrocarbons mixed with steam, hydrogen and possiblyother constituents, such as carbon monoxide, carbon dioxide, andpossibly also some nitrogen and argon. Typically, the feed gas let intothe reactor system has a predetermined ratio of hydrocarbon gas, steamand hydrogen, and potentially also carbon dioxide.

Moreover, the term “steam reforming” is meant to denote a reformingreaction according to one or more of the following reactions:

CH₄+H₂O↔CO+3H₂  (i)

CH₄+2H₂O↔CO₂+4H₂  (ii)

CH₄+CO₂↔2CO+2H₂  (iii)

Reactions (i) and (ii) are steam methane reforming reactions, whilstreaction (iii) is the dry methane reforming reaction.

For higher hydrocarbons, viz. C_(n)H_(m), where n≥2, m≥4, equation (i)is generalized as:

C_(n)H_(m) +nH₂O↔nCO+(n+m/2)H₂  (iv)

-   -   where n≥2, m≥4.

Typically, steam reforming is accompanied by the water gas shiftreaction (v):

CO+H₂O↔CO₂+H₂  (v)

The term “steam methane reforming” is meant to cover the reactions (i)and (ii), the term “steam reforming” is meant to cover the reactions(i), (ii) and (iv), whilst the term “methanation” covers the reversereaction of reaction (i). In most cases, all of these reactions (i)-(v)are at, or close to, equilibrium at the outlet from the reactor system.

The term “prereforming” is often used to cover the catalytic conversionof higher hydrocarbons according to reaction (iv). Prereforming istypically accompanied by steam reforming and/or methanation (dependingupon the gas composition and operating conditions) and the water gasshift reaction. Prereforming is often carried out in adiabatic reactorsbut may also take place in heated reactors.

The steam reforming reaction is highly endothermic. High temperaturestypically in excess of 800-850° C. are needed to reach acceptableconversions of the methane in the feed. A SMR consists of a number oftubes filled with catalyst pellets placed inside a furnace. The tubesare typically 10-13 meters long and will typically have an innerdiameter between 80 and 160 mm. Burners placed in the furnace providethe required heat for the reactions by combustion of a fuel gas. Amaximum average heat flux of 80000-90000 kcal/h/m² of inner tube surfaceis not uncommon. There is a general limitation to the obtainable heatflux due to mechanical constraints and the capacity is thereforeincreased by increasing the number of tubes and the furnace size. Moredetails on the SMR type reactor system can be found in the art, e.g.“Synthesis gas production for FT synthesis”; Chapter 4, p. 258-352,2004. As used herein, the abbreviation “SMR” is meant to denote anexternally fired tubular steam methane reformer ad described above.

Typically, the feed gas will have undergone desulfurization to removesulfur therein and thereby avoid deactivation of the catalysts in theprocess, prior to being inlet into the reactor system.

Optionally, the hydrocarbon gas will together with steam, andpotentially also hydrogen and/or other components such as carbondioxide, also have undergone prereforming according to reaction (iv) ina temperature range of ca. 350-550° C. to convert higher hydrocarbons asan initial step in the process, normally taking place downstream thedesulfurization step. This removes the risk of carbon formation fromhigher hydrocarbons on catalyst in the subsequent process steps.Optionally, carbon dioxide or other components may also be mixed withthe gas leaving the prereforming step to form the feed gas.

Typically, the feed gas entering into the reactor system has beenpreheated. However, due to the heat flux that can be provided by thestructured catalyst, the feed gas entering the reactor system can berelatively cold. Thus, preheating the feed gas to a temperature betweenabout 200 to about 450° C. may be sufficient.

The term “electrically conductive” is meant to denote materials with anelectrical resistivity in the range from: 10⁻⁵ to 10⁻⁸ Ω·m at 20° C.Thus, materials that are electrically conductive are e.g. metals likecopper, silver, aluminum, chromium, iron, nickel, or alloys of metals.Moreover, the term “electrically insulating” is meant to denotematerials with an electrical resistivity above 10 Ω·m at 20° C., e.g. inthe range from 10⁹ to 10²⁵ Ω·m at 20° C.

When the reactor system comprises a heat insulation layer between thestructured catalyst and the pressure shell, appropriate heat andelectrical insulation between the structured catalyst and the pressureshell is obtained. The presence of heat insulating layer between thepressure shell and the structured catalyst assists in avoiding excessiveheating of the pressure shell, and assists in reducing thermal losses tothe surroundings. The temperatures of the structured catalyst may reachup to about 1300° C., at least at some parts thereof, but by using theheat insulation layer between the structured catalyst and the pressureshell the temperature of the pressure shell can be kept at significantlylower temperatures of say 500° C. or even 200° C., which is advantageousas typical construction steel materials typically are unsuitable forpressure bearing application at temperatures above 1000° C. Moreover, aheat insulating layer between the pressure shell and the structuredcatalyst assists in control of the electrical current within the reactorsystem, since heat insulation layer is also electrically insulating. Theheat insulation layer could be one or more layers of solid material,such as ceramics, inert material, refractory material or a gas barrieror a combination thereof. Thus, it is also conceivable that a purge gasor a confined gas constitutes or forms part of the heat insulationlayer.

Moreover, it should be noted that the term “heat insulating material” ismeant to denote materials having a thermal conductivity of about 10W·m⁻¹·K⁻¹ or below. Examples of heat insulating materials are ceramics,refractory material, alumina based materials, zirconia based materialsand similar.

Advantageously, any relevant gaps between the structured catalyst, theheat insulation layer, the pressure shell, and/or any other componentsinside the reactor system is filled with inert material, e.g. in theform of inert pellets. Such gaps are e.g. a gap between the lower sideof the structured catalyst and the bottom of the pressure shell and agap between the sides of the structured catalyst and the insulationlayer covering the inner sides of the pressure shell. The inert materialmay e.g. be a ceramic material in the form of pellets or tiles. Theinert material assists in controlling the gas distribution through thereactor system and in controlling the flow of the gas through thestructured catalyst. Moreover, the inert material typically has a heatinsulating effect.

In an embodiment, the pressure shell has a design pressure of between 5bar and 30 bar. A pressure shell having a design pressure of about 5-15bar is for example well suited for small scale configuration. As thehottest part of the reactor system is the structured catalyst which willbe surrounded by heat insulation layer and within the pressure shell ofthe reactor system, the temperature of the pressure shell can be keptsignificantly lower than the maximum process temperature. This allowsfor having a relative low design temperature of the pressure shell ofe.g. 700° C. or 500° C. or preferably 300° C. or 200° C. of the pressureshell whilst having maximum process temperatures of 900° C. or even1100° C. or even up to 1300° C. on the structured catalyst. Materialstrength is higher at the lower of these temperatures (corresponding tothe design temperature of the pressure shell as indicated above) whichmeans that in contrast to the externally heated steam methane reformingreactor, such as a top fired or side fired SMR, the current reactorsystem can be designed for high(er) pressure operation. In an SMR themaximum tube wall temperature may be limited to ca. 1000° C. Anotheradvantage is that the lower design temperature compared to an SMR meansthat in some cases the thickness of the pressure shell can be decreasedthus saving costs.

In an embodiment, the pressure shell has a design pressure of between 30bar and 200 bar, preferably between 80 and 180 bar.

The reactor system of the invention may be part of a plant, such as ahydrogen plant. Such a plant may advantageously comprise one or morecompressors and/or pumps upstream the reactor system of the invention.The compressors/pumps are arranged to compress the feed to a pressure ofbetween 30 and 200 bar upstream the reactor system. The constituents ofthe feed, viz. steam, hydrogen and hydrocarbon feed gas, may becompressed individually and fed individually into the reactor system ofthe invention. When the feed is pressurized upstream the reactor systemof the invention and the reactor system comprises a pressure shellhaving a design pressure of between 30 and 200 bar, compressiondownstream of the reactor system of the invention may be made simpler oravoided completely. For a hydrogen plant integrated in a refinery plantwhere the hydrogen product is used for hydrotreating a hydrogencompressor to the hydrotreater may be avoided if the product gas fromthe reactor system has an outlet pressure of about 150-200 bar.

In an embodiment, the resistivity of the macroscopic structure isbetween 10⁻⁶ Ω·m and 10⁻⁷ Ω·m. A material with a resistivity within thisrange provides for an efficient heating of the structured catalyst whenenergized with a power source. Graphite has a resistivity of about 10⁻⁶Ω·m at 20° C., kanthal has a resistivity of about 10⁻⁶ Ω·m at 20° C.,whilst stainless steel has a resistivity of about 10⁻⁷ Ω·m at 20° C.Kanthal is the trademark for a family of iron-chromium-aluminum (FeCrAl)alloys. The macroscopic structure may for example be made of FeCrAlloyhaving a resistivity of ca. 1.5·10⁻⁶ Ω·m at 20° C.

It should be noted, that the system of the invention may include anyappropriate number of power supplies and any appropriate number ofconductors connecting the power supply/supplies and the macroscopicstructure(s) of the structured catalyst.

According to an embodiment of the reactor system, each of the at leasttwo conductors are led through a pressure shell in a fitting so that theat least two conductors are electrically insulated from the pressureshell. The fitting may be, partly, of a plastic and/or ceramic material.The term “fitting” is meant to denote a device which allows formechanically connecting two pieces of hardware in a pressure bearingconfiguration. Thereby, the pressure within the pressure shell may bemaintained even though the at least two conductors are lead through it.Non-limiting examples of the fittings may be an electrically insulatingfitting, a dielectric fitting, a power compression seal, a compressionfitting or a flange. The pressure shell typically comprises side walls,end walls, flanges, and possibly further parts. The term “pressureshell” is meant to cover any of these components.

The fittings are positioned in connection with the first end of themacroscopic structure. For example, the fittings are positioned upstreamthe first end of the macroscopic structure as seen in the direction ofthe feed gas. Hereby the temperature of the fittings themselves will bekept relatively cold. The combination of heat insulation and thefittings in the relatively cold end of the pressure shell renders itpossible to provide a pressure within the pressure shell of more than 5bar, despite of the fittings through the walls of the pressure shell anddespite the fact that the maximum temperature of the structured catalystmay reach about 950° C. If the fittings were not kept relatively cold,there would be a risk of mechanical errors such as deformations, and aleakage of gas from the pressure shell would be probable. Moreover,electrical connection between the at least two conductors and thepressure shell should be avoided. To this end, it is important to avoidexcessive temperatures of the fitting. As an example, the fitting maycomprise a polymer as well as a compression fitting.

In an embodiment, the pressure shell further comprises one or moreinlets close to or in combination with at least one of the fittings inorder to allow a cooling gas to flow over, around, close to or inside atleast one conductor within the pressure shell. Hereby, the conductorsare cooled and thus the temperature that the fitting experiences is keptdown. If the cooling gas is not used, the conductors may be heated bythe feed gas to the reactor system, resistance heating of conductor dueto the applied current, and/or heat conduction from the structuredcatalyst. The cooling gas could e.g. be hydrogen, nitrogen, steam,carbon dioxide, or mixtures thereof. The temperature of the cooling gasat entry into the pressure shell may be e.g. about 100° C. or 200° C. or250° C. In an embodiment, the conductor(s) is (are) hollow so that thecooling gas may flow through the conductor(s) and cool it (them) fromwithin. By keeping the temperature of the fitting low, e.g. at around100-200° C., it is easier to have a leak tight configuration. In anembodiment, a part of the feed gas, such as carbon dioxide and/or steam,is fed to the pressure shell as the cooling gas. In another embodiment,part of the feed gas or a gas with the same composition as the feed gasis used as cooling gas.

In an embodiment, the reactor system further comprises an inner tube inheat exchange relationship with the structured catalyst, where the innertube is adapted to withdraw a product gas from the structured catalystso that the product gas flowing through the inner tube or tubes is inheat exchange relationship with the gas flowing through the structuredcatalyst, but electrically separated from the structured catalyst. Thisis a layout which here is denoted a bayonet reactor system. In thislayout the product gas within the inner tube assists in heating theprocess gas flowing through the structured catalyst. The electricalinsulation between the inner tube and the structured catalyst could begas in the form of a gap or distance between the inner tube and thestructured catalyst or inert material loaded around the inner tube andthe structured catalyst. The gas may pass through the structuredcatalyst in an up-flow or a down-flow direction. Even though theelectrical insulation between the inner tube and the structured catalystalso provides for thermal insulation, such a thermal insulation effectis never complete and some heat transfer will take place over theelectrical insulation.

In an embodiment, the connection between the structured catalyst and theat least two conductors is a mechanical connection, a welded connection,a brazed connection or a combination thereof. The structured catalystmay comprise terminals physically and electrically connected to thestructured catalyst in order to facilitate the electrical connectionbetween the macroscopic structure of the structured catalyst and the atleast two conductors. The term “mechanical connection” is meant todenote a connection where two components are held together mechanically,such as by a threaded connection or by clamping, so that a current mayrun between the components.

In an embodiment, the macroscopic structures in an array of macroscopicstructures may be electrically connected to each other. The connectionbetween the two or more macroscopic structures may be by mechanicalconnection, clamping, soldering, welding, or any combination of theseconnection methods. Each macroscopic structure may comprise terminals inorder to facilitate the electrical connections. The two or moremacroscopic structures may be connected to the power supply in serial orparallel connection. The electrical connection between the two or moremacroscopic structures is advantageously coherent and uniform along theconnection surface between the two or more macroscopic structures, sothat the two or more macroscopic structures act as a single coherent orconsistently intra-connected material; hereby, uniform electricalconductivity throughout the two or more macroscopic structures isfacilitated. Alternatively, or additionally, the structured catalyst maycomprise an array of macroscopic structures which are not electricallyconnected to each other. Instead, two or more macroscopic structures areplaced together within the pressure shell, but not connectedelectrically to each other. In this case, the structured catalyst thuscomprises macroscopic structures connected in parallel to the powersupply.

A ceramic coating, with or without catalytically active material, may beadded directly to a metal surface by wash coating. The wash coating of ametal surface is a wellknown process; a description is given in e.g.Cybulski, A., and Moulijn, J. A., Structured catalysts and reactors,Marcel Dekker, Inc, New York, 1998, Chapter 3, and references herein.The ceramic coat may be added to the surface of the macroscopicstructure and subsequently the catalytically active material may beadded; alternatively, the ceramic coat comprising the catalyticallyactive material is added to the macroscopic structure.

Extruding and sintering, or 3D printing and sintering, a macroscopicstructure results in a uniformly and coherently shaped macroscopicstructure, which can afterwards be coated with the ceramic coating.

The macroscopic structure and the ceramic coating may have been sinteredin an oxidizing atmosphere in order to form chemical bonds between theceramic coating and the macroscopic structure; this provides for anespecially high heat conductivity between the macroscopic structure andthe catalytically active material supported by the ceramic coating.Thereby, the structured catalyst is compact in terms of heat transfer tothe active catalytic site, and a reactor system housing the structuredcatalyst may be compact and limited mainly by the rate of the chemicalreaction. There is no heat transfer from outside the pressure shell tothe structured catalyst as would be the case through the tube walls tothe catalyst within the tubes for the SMRs used in the art.

In an embodiment, the structured catalyst has at least one electricallyinsulating part arranged to increase the current path between theconductors to a length larger than the largest dimension of thestructured catalyst. The provision of a current path between theconductors larger than the largest dimension of the structured catalystmay be by provision of electrically insulating part(s) positionedbetween the conductors and preventing the current running through somepart of the structured catalyst. Such electrically insulating parts arearranged to increase the current path and thus increase the resistancethrough the structured catalyst. Hereby, the current path through thestructured catalyst can be e.g. more than 50%, 100%, 200%, 1000%, oreven 10000% longer than the largest dimension of the structuredcatalyst.

Moreover, such electrically insulating parts are arranged to direct thecurrent from one conductor, which is closer to the first end of thestructured catalyst than to the second end, towards the second end ofthe structured catalyst and back to a second conductor closer to thefirst end of the structured catalyst than to the second end. Preferably,the current is arranged to run from the first end of the structuredcatalyst to the second and back to the first end. As seen in thefigures, the first end of the structured catalyst is the top endthereof. The arrow indicated “z” in FIGS. 5-7 indicates a z-axis alongthe length of the structured catalyst. The principal current paththroughout the structured catalyst will have a positive or negativevalue of z-coordinate of the accompanied current density vector alongmost of the length of the current path. By principal current path ismeant the path of the electrons through a macroscopic structure of thestructured catalyst with the highest current density. The principalcurrent path can also be understood as the path having the minimumlength through the macroscopic structure of the structured catalyst.Seen geometrically, the principal current path can be quantified as thelargest current density vector within a plane perpendicular to the gasflow direction of a coherent section of the macroscopic structure. Atthe bottom of the structured catalyst, as shown in the figures, thecurrent will turn, and here the z-coordinate of the accompanied currentdensity vector will be zero.

As used herein, the term coherent section is meant to denote across-section area of the macroscopic structure wherein all walls of thecoherent section are geometrically connected to one or more other wallsof the coherent section within the same plane.

In an embodiment, the structured catalyst has at least one electricallyinsulating part arranged to direct a current through the structuredcatalyst in order to ensure that for at least 70% of the length of saidstructured catalyst, a current density vector of a principal currentpath has a non-zero component value parallel to the length of saidstructured catalyst. Thus, for at least 70% of the length of thestructured catalyst, the current density vector will have a positive ornegative component value parallel to the length of the structuredcatalyst. Thus, for at least 70%, e.g. for 90% or 95%, of the length ofstructured catalyst, viz. along the z-axis of the structured catalyst asseen in FIGS. 5 to 10, the current density vector of a principal currentpath will have a positive or negative value along the z-axis. This meansthat the current is forced from the first end of the structured catalysttowards the second end, and subsequently is forced towards the first endagain. The temperature of the gas entering the first end of thestructured catalyst and the endothermic steam reforming reaction takingplace over the structured catalyst absorbs heat from the structuredcatalyst. For this reason, the first end of the structured catalystremains colder than the second end, and by ensuring that the currentdensity vector of the principal current path has a non-zero componentvalue parallel to the length of said structured catalyst, this takesplace with a substantially continuously increasing temperature profile,which gives a controllable reaction front. In an embodiment the currentdensity vector has a non-zero component value parallel to the length ofsaid structured catalyst in 70% of the length of said structuredcatalyst, preferably 80%, more preferably 90%, and even more preferably95%. It should be noted that the term “the length of the structuredcatalyst” is meant to denote the dimension of the structured catalyst inthe direction of the gas flow. In the structured catalysts as shown inthe figures, the length is the longitudinal direction, viz. the longestdimension thereof. This is indicated by the arrow denote z in some ofthe figures.

Non-limiting examples of insulating parts are cuts, slits, or holes inthe structure. Optionally, a solid insulating material such as ceramicsin cuts or slits in the structure can be used. In a case where the solidinsulating material is a porous ceramic material, the catalyticallyactive material may advantageously be incorporated in the pores, by e.g.impregnation. A solid insulating material within a cut or slit assistsin keeping the parts of the structured catalyst on the sides of the cutor slit from each other. As used herein, the term “largest dimension ofthe structured catalyst” is meant to denote the largest inner dimensionof the geometrical form taken up by the structured catalyst. If thestructured catalyst is box-formed, the largest dimension would be thediagonal from one corner to the farthest corner, also denoted the spacediagonal.

It should be noted that even though the current path through thestructured catalyst may be arranged to be twist or winded through thestructured catalyst due to the electrically insulating parts arranged toincrease the current path, the gas passing through the reactor system isinlet at one end of the reactor system, passes through the structuredcatalyst once before being outlet from the reactor system. Inertmaterial is advantageously present in relevant gaps between thestructured catalyst and the rest of the reactor system to ensure thatthe gas within the reactor system passes through the structured catalystand the catalytically active material supported thereby.

In an embodiment the length of the gas passage through the structuredcatalyst is less than the length of the passage of current from oneconductor through the structured catalyst and to the next conductor. Theratio of the length of the gas passage to the length of the currentpassage may be less than 0.6, or 0.3, 0.1, or even down to 0.002.

In an embodiment, the structured catalyst has at least one electricallyinsulating part arranged to make the current path through the structuredcatalyst a zigzag path. Here, the terms “zigzag path” and “zigzag route”is meant to denote a path that has corners at variable angles tracing apath from one conductor to another. A zigzag path is for example a pathgoing upwards, turning, and subsequently going downwards. A zig-zag pathmay have many turns, going upwards and subsequently downwards many timesthrough the structured catalyst, even though one turn is enough to makethe path a zigzag path.

It should be noted that the insulating parts arranged to increase thecurrent path are not necessarily related to the ceramic coating on themacroscopic structure; even though this ceramic coating is alsoconsidered electrically insulating, it does not change the length of thecurrent path between the conductors connected to the macroscopicstructure.

In an embodiment, the macroscopic structure has a plurality ofnear-parallel or parallel channels, a plurality of non-parallelchannels, and/or a plurality of labyrinthic channels, where the channelshave walls defining the channels. Thereby, several different forms ofthe macroscopic structure can be used as long as the surface area of thestructured catalyst exposed to the gas is as large as possible. In apreferred embodiment, the macroscopic structure has parallel channels,since such parallel channels render a structured catalyst with a verysmall pressure drop. In a preferred embodiment, parallel longitudinalchannels are skewed in the longitudinal direction of the macroscopicstructure. In this way molecules of the gas flowing through themacroscopic structure will mostly tend to hit a wall inside the channelsinstead of just flowing straight through a channel without being incontact with a wall. The dimension of the channels should be appropriatein order to provide a macroscopic structure with a sufficientresistivity. For example, the channels could be quadratic (as seen incross section perpendicular to the channels) and have a side length ofthe squares of between 1 and 3 mm; however, channels having a maximumextent in the cross section of up to about 4 cm are conceivable.Moreover, the thickness of the walls should be small enough to provide arelatively large electrical resistance and large enough to providesufficient mechanical strength. The walls may e.g. have a thickness ofbetween 0.2 and 2 mm, such as about 0.5 mm, and the ceramic coatingsupported by the walls has a thickness of between 10 μm and 500 μm, suchas between 50 μm and 200 μm, such as 100 μm. In another embodiment themacroscopic structure of the structured catalyst is cross-corrugated.

In general, when the macroscopic structure has parallel channels, thepressure drop from the inlet to the outlet of the reactor system may bereduced considerably compared to a reactor where the catalyst materialis in the form of pellets such as a standard SMR.

In an embodiment, the reactor system further comprises a bed of a secondcatalyst material upstream the structured catalyst within the pressureshell. Here, the term “upstream” is seen from the flow direction of thefeed gas. Thus, the term “upstream” is here meant to denote that thefeed gas is directed through the bed of second catalyst material priorto reaching the structured catalyst. This provides for a situation wherethe second catalyst material can be arranged for prereforming the feedgas (according to reaction (iv) above), so that the reactor systemprovides prereforming and steam reforming within one pressure shell.This can also provide a situation where the hydrocarbons in the feed gasreact with steam and/or CO₂ over the second catalyst material (such asaccording to reactions (i)-(v) above) and that the process gas to thestructured catalyst then has a lower content of hydrocarbons than thefeed gas to the second catalyst material. The second catalyst canalternatively or additionally be a catalyst arranged for also capturingsulfur compounds in the feed gas. No specific heating needs to beprovided to the bed of second catalyst material; however, the bed ofsecond catalyst material may be heated indirectly if it is in closeproximity to the structured catalyst. Alternatively, the second catalystmaterial may be heated.

In an embodiment, the reactor system further comprises a third catalystmaterial in the form of catalyst pellets, extrudates, or granulatesloaded into the channels of the structured catalyst. In this embodiment,the reactor system will thus have a catalytically active material in thecoating of the macroscopic structure as well as a third catalystmaterial in the form catalyst pellets, extrudates, or granulates withinthe channels of the structured catalyst. This allows for boosting thecatalytic reactivity within the channels, or segments of these, of thestructured catalyst. In order to clarify the terminology used here, itis noted that the term “structured catalyst” may also be denoted “afirst catalyst material” to distinguish it from the second and/or thirdand/or fourth catalyst material.

The pellets are e.g. prepared in a dimension to loosely match the sizeof channels to form a single string of pellets stacked upon each otherwithin a channel of the macroscopic structure. Alternatively, thepellets, extrudates or granulates may be prepared in a dimensionsignificantly smaller than the channel size to form a packed bed insideeach channel. As used herein, the term “pellet” is meant to denote anywell-defined structure having a maximum outer dimension in the range ofmillimeters or centimeters, while “extrudate” and “granulate” are meantto define a catalyst material with a maximum outer dimension definedwithin a range.

In an embodiment a bed of fourth catalyst material is placed within thepressure shell and downstream the structured catalyst. Such fourthcatalyst material may be in the form of catalyst pellets, extrudates orgranulates. This provides for a situation where the fourth catalystmaterial can be arranged for lowering the approach to equilibrium of thegas leaving the structured catalyst by making a pseudo adiabaticequilibration of the steam reforming reaction.

In an embodiment the second, third, and fourth catalyst material arecatalyst materials suitable for the steam reforming reaction, theprereforming reaction, or the water gas shift reaction. Examples ofrelevant such catalysts are Ni/MgAl₂O₄, Ni/CaAl₂O₄, Ni/Al₂O₄, andCu/Zn/Al₂O₃. In a configuration where a combination of the second,third, and fourth catalyst material is included in the reactor system,the catalyst of each catalyst material can be different.

In an embodiment, the material of the macroscopic structure is chosen asa material arranged to supply a heat flux of 500 W/m² to 50000 W/m² byresistance heating of the material. Preferably, resistance heating ofthe material supplies a heat flux of between 5 kW/m² and 12 kW/m², forexample between 8 kW/m² and 10 kW/m². The heat flux is given as heat pergeometric surface area of the surface exposed to the gas.

In an embodiment, the geometric surface area of the macroscopicstructure is between 100 and 3000 m²/m³, such as between 500 and 1100m²/m³. The heat flux from the material is advantageously chosen to matchthe reactivity of the catalytically active material.

In an embodiment the structured catalyst comprises a first part arrangedto generate a first heat flux and a second part arranged to generate asecond heat flux, where the first heat flux is lower than the secondheat flux, and where the first part is upstream the second part. Here,the term “the first part is upstream the second part” is meant todenote, that the gas fed into the reactor system reaches the first partbefore the gas reaches the second part. The first part and second partof the structured catalyst may be two different macroscopic structuressupporting ceramic coating supporting catalytically active material,where the two different macroscopic structures may be arranged togenerate different heat fluxes for a given electrical current andvoltage. For instance, the first part of the structured catalyst mayhave a large surface area, whilst the second part of the structuredcatalyst has a smaller surface area. This may be accomplished byproviding a structured catalyst in the second part having a smallercross sectional area than the cross sectional area of the first part.Alternatively, the current path through the first part of the structuredcatalyst may be more straight than the current path through the secondpart of the structured catalyst, thus making the current twist and windmore through the second part than through the first part of thestructured catalyst, whereby the current generates more heat in thesecond part of the structured catalyst than in the first part. Asmentioned before, slits or cuts in the macroscopic structure may makethe current path zigzag through the macroscopic structure. It should benoted, that the first and second part of the structured catalyst mayexperience different electrical currents and voltages in order to beable to supply different heat fluxes. However, the different heat fluxesof the first and second part may also be achieved by supplying the sameelectrical current and voltage through/over the first and second part,due to different physical properties of the first and second part asindicated above.

In an embodiment, the reactor system further comprises a control systemarranged to control the electrical power supply to ensure that thetemperature of the gas exiting the pressure shell lies in apredetermined range and/or to ensure that the conversion of hydrocarbonsin the feed gas lies in a predetermined range and/or to ensure the drymole concentration of methane lies in a predetermined range and/or toensure the approach to equilibrium of the steam reforming reaction liesin a predetermined range. Typically, the maximum temperature of the gaslies between 500° C. and 1000° C., such as between 850° C. and 1000° C.,such as at about 950° C., but even higher temperatures are conceivable,e.g. up to 1300° C. However, the maximum temperature of the gas exitingthe reactor system may be as low as 500° C., for instance in a casewhere the reactor system is of the bayonet type. The maximum temperatureof the gas will be achieved close to the most downstream part of thestructured catalyst as seen in the flow direction of the feed gas.However, when a bayonet type layout is used, the maximum temperature ofthe gas exiting the reactor system may be somewhat lower, due to theheat exchange with the feed gas; the maximum temperature of the gasexiting a bayonet type reactor system according to the invention may bebetween 500 and 900° C. The control of the electrical power supply isthe control of the electrical output from the power supply. The controlof the electrical power supply may e.g. be carried out as a control ofthe voltage and/or current from the electrical power supply, as acontrol of whether the electrical power supply is turned on or off or asa combination hereof. The power supplied to the structured catalyst canbe in the form of alternating current or direct current.

The voltage between the at least two conductors can be any appropriatevoltage arranged to provide the desired heat flux. If the voltage is toolow, the heat flux may become too low, and if the voltage is too high,the risk of electric arcs is increased. Exemplary values are e.g. avoltage between 50 and 4000 V, such as between 100 and 1000 V. Suchvalues will render the compactness of the macroscopic structure and thusof the reactor system possible. Moreover, the current running betweenconductors through the macroscopic structure can be any appropriatecurrent which together with the chosen voltage will provide the desiredheat flux. The current may e.g. be between 100 and 2000 A, such asbetween 200 and 1500 A.

The predetermined temperature range of the gas exiting the pressureshell/the reactor system is preferably the range from 500 to 1300° C.,preferably in the range from 800° C. to 1150° C., such as 900° C. to1000° C. Preferably, the range of approach to equilibrium of the steammethane reforming reaction is between 1 and 60° C., more preferablybetween 5 and 30° C. or most preferably between 5 and 20° C.

In order to control the temperature of a reaction, the heatadded/removed from a reactor system needs to be balanced against theheat consumed/produced by the chemical reaction. The addition/removal ofheat needs to be balanced against the rate of reaction and especiallythe approach to equilibrium as defined by β, where β is the ratiobetween the reaction quotient and the equilibrium constant of areaction. A value of β approaching 1 means the reaction mixture is closeto equilibrium and values approaching 0 means the reaction mixture isfar from equilibrium. In general, it is desirable to have as high a rateof reaction as possible, which is achieved at a low β, as long as thetemperature can be sufficiently controlled in parallel by balancing theenergy added.

In the case of the endothermic steam methane reforming reaction, heatneeds to be added to ensure the reaction continues to proceed asotherwise the reaction will be equilibrated and the β value willapproach 1 and the reaction will slow down. However, on the other side,it is undesirable if the temperature increases faster than the rate ofreaction can follow as exposing unconverted hydrocarbons to hightemperatures can result in carbon formation. A good way to follow thisbehavior is by the approach to equilibrium. The approach to equilibriumof the steam reforming reaction is found by initially calculating thereaction quotient (Q) of the given gas as:

$Q = {\frac{y_{CO} \cdot y_{H_{2}}^{3}}{y_{CH_{4}} \cdot y_{H_{2}O}} \cdot P^{2}}$

Here y_(j) is the molar fraction of compound j, and P is the totalpressure in bar. This is used to determine the equilibrium temperature(T_(eq)) at which the given reaction quotient is equal to theequilibrium constant:

Q=K_(SMR)(T_(eq))

where K_(SMR) is the thermodynamic equilibrium constant of the steammethane reforming reaction. The approach to equilibrium of the steammethane reforming (ΔT_(app,SMR)) reaction is then defined as:

ΔT_(app,SMR)=T−T_(eq)

Where T is the bulk temperature of the gas surrounding the catalystmaterial used, such as the structured catalyst.

To ensure good performance of a steam reforming catalyst, it isdesirable that the catalyst continuously works towards decreasingΔT_(app,SMR). Classically, large scale industrial SMRs have beendesigned to obtain an approach to equilibrium of 5-20° C. at the outletthereof.

With the current invention it is possible to control the heat flux andmatch this directly to the kinetic performance of the structuredcatalyst, as these are independent to some extent.

In an embodiment, the structured catalyst within the reactor system hasa ratio between the area equivalent diameter of a horizontal crosssection through the structured catalyst and the height of the structuredcatalyst in the range from 0.1 to 2.0. The area equivalent diameter ofthe cross section through the reactor system is defined as the diameterof a circle of equivalent area as the area of the cross section. Whenthe ratio between the area equivalent diameter and the height of thestructured catalyst is between 0.1 and 2.0, the pressure shell housingthe structured catalyst may be relatively small compared to currentSMRs. Each reactor system may process a larger amount of feed gas thanis possible in one tube of an SMR. Hereby, the amount of outside pipingto the reactor system may be reduced compared to a current SMR, andthereby the cost of such piping is reduced. Typically, the gas flowsthrough the reactor system in an upflow or downflow direction, so thatthe gas flows through channels in the structured catalyst along theheight thereof. When the structured catalyst comprises a number of or anarray of macroscopic structures, the individual macroscopic structureswithin the array may be placed side by side, on top of each other or ina combination thereof. It is stressed, that when the structured catalystcomprises more than one macroscopic structures, the dimensions of thestructured catalyst are the dimensions of the more than one macroscopicstructures. Thus, as an example, if the structured catalyst comprisestwo macroscopic structures, each having the height h, put on top of eachother, the height of the structured catalyst is 2 h.

The volume of the structured catalyst is chosen in consideration of thedesired approach to equilibrium and/or temperature and/or hydrocarbonsconversion and/or dry mole concentration of hydrocarbons in the productgas and/or temperature out of the reactor system correlated to the heatgeneration capacity of the macroscopic structure and/or to ensure thedry mole concentration of hydrocarbons in the product gas lies in apredetermined range and/or to ensure the approach to equilibrium of thesteam methane reforming reaction (reaction (i)) lies in a predeterminedrange.

In an embodiment, the height of the reactor system is between 0.5 and 7m, more preferably between 0.5 and 3 m. Exemplary values of the heightof the reactor system is a height of less than 5 meters, preferably lessthan 2 m or even 1 m. The dimensions of the reactor system and of thestructured catalyst within the reactor system are correlated; of course,the pressure shell and heat insulation layer render the reactor systemsomewhat larger than the structured catalyst itself. For comparison,industrial scale SMRs are typically constructed of catalyst tubes havinga length of 10 m or above to maximize external surface area of thetubes. The present invention is advantageous in that such confinement inthe design of the reactor system are superfluous.

As used herein the term “reactor system comprising a structuredcatalyst” is not meant to be limited to a reactor system with a singlemacroscopic structure. Instead, the term is meant to cover both astructured catalyst with a macroscopic structure, ceramic coating andcatalytically active material as well as an array of such macroscopicstructures.

Another aspect of the invention relates to a process for carrying outsteam reforming of a feed gas comprising hydrocarbons in a reactorsystem comprising a pressure shell housing a structured catalystarranged to catalyze steam reforming of a feed gas comprisinghydrocarbons. The structured catalyst comprising a macroscopic structureof an electrically conductive material, and the macroscopic structuresupports a ceramic coating. The ceramic coating supports a catalyticallyactive material and the reactor system is provided with heat insulationbetween the structured catalyst and the pressure shell. The reactorsystem is provided with heat insulation between the structured catalystand the pressure shell. The process comprises the following steps:

-   -   pressurizing a feed gas comprising hydrocarbons to a pressure of        at least 5 bar,    -   supplying the pressurized feed gas to the reactor system,    -   allowing the feed gas to undergo steam reforming reaction over        the structured catalyst and outletting a product gas from the        reactor system, and    -   supplying electrical power via electrical conductors connecting        an electrical power supply placed outside the pressure shell to        the structured catalyst, allowing an electrical current to run        through the macroscopic structure, thereby heating at least part        of the structured catalyst to a temperature of at least 500° C.

The process provides advantages similar to those outlined for thereactor system. The product gas is a synthesis gas. Synthesis gas is agas comprising carbon monoxide and hydrogen as well as other componentssuch steam, carbon dioxide, and methane. However, the process maycomprise further steps carried out on the product gas, such aspurification, pressurization, heating, cooling, water gas shiftreaction, etc. to provide the final product gas for an applicationdownstream the reactor system of this invention.

It should be noted that the feed gas may comprises individual feedgasses, such as steam, hydrocarbon gas, carbon dioxide and hydrogen, andthat the step of pressurizing the feed gas may comprise pressurizingindividual feed gasses individually. Moreover, it should be noted thatthe order in which the steps of the process are written are notnecessarily the order in which the process steps take place, in that twoor more steps may take place simultaneously, or the order may bedifferent that indicated above.

In an embodiment the process comprises the step of pressurizing the gasupstream the pressure shell to a pressure of up to at least 5 bar. Apressure shell with a design pressure of between 5 and 15 bar is wellsuited for small scale configuration. For larger scale configurations,the pressure shell may have a design pressure of e.g. 15 bar, 30 bar oreven up to 50 bar. Even design pressures of up to 150 or 200 bar areconceivable.

In an embodiment of the process according to the invention, thetemperature of the feed gas let into the reactor system is between 200°C. and 700° C. For externally heated SMRs, the temperature of the feedgas would normally be heated to a temperature between 450° C. and 650°C.; however, since the reactor system used in the process is aninternally heated reactor system, the temperature of the feed gas may beas low as 200° C. However, in all embodiments the temperature and thepressure of the feed gas are adjusted to ensure that the feed gas isabove the dew point.

In an embodiment of the process of the invention, the structuredcatalyst is heated so that the maximum temperature of the structuredcatalyst lies between 500° C. and 1300° C. Preferably, the maximumtemperature of the structured catalyst lies between 700° C. and 1100°C., such as between 900° C. and 1000° C. The maximum temperature of thestructured catalyst depends upon the material of the macroscopicstructure; thus, if the macroscopic structure is of FeCrAlloy, whichmelts at a temperature of between 1380° C. and 1490° C. (depending onthe actual alloy), the maximum temperature should be somewhat below themelting point, such as at about 1300° C. if the melting point of themacroscopic structure is at about 1400° C., as the material will becomesoft and ductile when approaching the melting point. The maximumtemperature may additionally be limited by the durability of the coatingand catalytically active material.

In an embodiment the process according to the invention furthercomprises the step of inletting a cooling gas through an inlet throughthe pressure shell in order to allow a cooling gas to flow over at leastone conductor and/or fitting. The cooling gas may advantageously behydrogen, nitrogen, steam, carbon dioxide or any other gas suitable forcooling the area or zone around the at least one conductor. A part ofthe feed gas, such as carbon dioxide and/or steam, may be fed to thepressure shell as the cooling gas.

In an embodiment of the process, the space velocity of gas, evaluated asflow of gas relative to the geometric surface area of the structuredcatalyst, is between 0.6 and 60 Nm³/m²/h, such as between 3 and 17Nm³/m²/h, or such as between 9 and 14 Nm³/m²/h. Given relative to theoccupied volume of the structured catalyst, the space velocity isbetween 700 Nm³/m³/h and 70000 Nm³/m³/h, such as between 3500 Nm³/m³/hand 20000 Nm³/m²/h, or such as between 11000 Nm³/m³/h and 16000Nm³/m³/h. Given as a space velocity relative to the volume of activecatalyst, i.e. the volume of the ceramic coat, it is between 6000Nm³/m³/h and 1200000 Nm³/m³/h. Operating within these ranges of thespace velocity allows for a desired conversion. It should be noted, thatthe space velocity of the gas is meant to denote the space velocity ofthe gas entering the reactor system, viz. both the feed gas and thecooling gas.

In an embodiment according to the invention, the process furthercomprises the step of inletting a cooling gas through an inlet throughthe pressure shell in order to allow a cooling gas to flow over at leastone conductor and/or fitting. The cooling gas may be any appropriategas; examples of such gasses are hydrogen, nitrogen, steam, carbondioxide, or mixtures thereof. The cooling gas may flow through theconductor(s) and cool it (them) from within; in this case, theconductor(s) need(s) to be hollow to accommodate the cooling gas flowingwithin it/them. Part of the feed gas or a gas with the same compositionas the feed gas may be used as cooling gas.

The following is a detailed description of embodiments of the inventiondepicted in the accompanying drawings. The embodiments are examples andare in such detail as to clearly communicate the invention. However, theamount of detail offered is not intended to limit the anticipatedvariations of embodiments; but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims.

SHORT DESCRIPTION OF THE FIGURES

FIG. 1a shows a cross section through an embodiment of the inventivereactor system with a structured catalyst comprising an array ofmacroscopic structures, in a cross section;

FIG. 1b shows the reactor system of FIG. 1a with a part of the pressureshell and heat insulation layer removed;

FIG. 2 is an enlarged view of a part of the reactor system;

FIGS. 3a and 3b show schematic cross sections through an embodiment ofthe inventive reactor system comprising a structured catalyst;

FIGS. 4 and 5 show an embodiment of a structured catalyst with an arrayof macroscopic structures as seen from above and from the side,respectively;

FIG. 6 shows an embodiment of the structured catalyst used in thereactor system of the invention;

FIGS. 7, and 8 show embodiments of a structured catalyst withconnectors;

FIG. 9a shows an embodiment of a structured catalyst for use in thereactor system of the invention;

FIG. 9b shows the current density of the structured catalyst shown inFIG. 9a as a function of the electrical effect transferred to thestructured catalyst;

FIG. 10 a schematic drawing of a cross-section through structuredcatalyst with electrically insulating parts;

FIGS. 11a and 11b show temperature and conversion profiles as a functionof electrical effect transferred to the structured catalyst;

FIGS. 12a and 12b show simulation results for temperatures and gascomposition along the length of the structured catalyst;

FIG. 13 shows the required maximum temperature within the reactor systemof the invention as a function of the pressure; and

FIG. 14 is a graph of the approach to equilibrium (ΔT_(app,SMR)) of thesteam methane reforming reaction for different gas flow rates over astructured catalyst.

DETAILED DESCRIPTION OF THE FIGURES

Throughout the Figures, like reference numbers denote like elements.

FIG. 1a shows a cross section through an embodiment of a reactor system100 according to the invention. The reactor system 100 comprises astructured catalyst 10, arranged as an array of macroscopic structures5. Each macroscopic structure 5 in the array is coated with a ceramiccoating impregnated with catalytically active material. The reactorsystem 100 moreover comprises conductors 40, 40′ connected to a powersupply (not shown in the Figures) and to the structured catalyst 10,viz. the array of macroscopic structures. The conductors 40, 40′ are ledthrough the wall of a pressure shell 20 housing the structured catalystand through insulating material 30 on the inner side of the pressureshell, via fittings 50. The conductors 40′ are connected to the array ofmacroscopic structures 5 by conductor contact rails 41.

In an embodiment, the electrical power supply supplies a voltage of 70Vand a current of 800 A. In another embodiment, the electrical powersupply supplies a voltage of 170V and a current of 2000 A. The currentis led through electrical conductors 40, 40′ to conductor contact rails41, and the current runs through the structured catalyst 10 from oneconductor contact rail 41, e.g. from the conductor contact rail seen tothe left in FIG. 1a , to the other conductor contact rail 41, e.g. theconductor contact rail seen to the right in FIG. 1a . The current can beboth alternating current, and e.g. run alternating in both directions,or direct current and run in any of the two directions.

The macroscopic structures 5 are made of electrically conductivematerial. Especially preferred is the alloy kanthal consisting ofaluminum, iron and chrome. The ceramic coating, e.g. an oxide, coatedonto the structure catalysts 5 is impregnated with catalytically activematerial. The conductors 40, 40′ are made in materials like iron,aluminum, nickel, copper, or alloys thereof.

During operating, a feed gas enters the reactor system 100 from above asindicated by the arrow 11 and exits the reactor system from the bottomthereof as indicated by the arrow 12.

FIG. 1b shows the reactor system 100 of FIG. 1a with a part of thepressure shell 20 and heat insulation 30 layer removed and FIG. 2 is anenlarged view of a part of the reactor system 100. In FIGS. 1b and 2 theconnections between conductors 40′ and conductor contact rails 41 areshown more clearly than in FIG. 1a . Moreover, it is seen that theconductors 40 are led through the walls of the pressure shell in afitting 50, and that the one conductor 40 is split up into threeconductors 40′ within the pressure shell. It should be noted, that thenumber of conductors 40′ may be any appropriate number, such as smallerthan three or even larger than three.

In the reactor system shown in FIGS. 1a, 1b and 2, the conductors 40,40′ are led through the wall of a pressure shell 20 housing thestructured catalysts and through insulating material 30 on the innerside of the pressure shell, via fittings 50. Feed gas for steamreforming is inlet into the reactor system 100 via an inlet in the upperside of the reactor system 100 as shown by the arrow 11, and reformedgas exists the reactor system 100 via an outlet in the bottom of thereactor system 100 as shown by the arrow 12. Moreover, one or moreadditional inlets (not shown in FIGS. 1a to 2) advantageously existclose to or in combination with the fittings 50. Such additional inletsallow a cooling gas to flow over, around, close to, or inside at leastone conductor within the pressure shell to reduce the heating of thefitting. The cooling gas could e.g. be hydrogen, nitrogen, steam, carbondioxide, or mixtures thereof. The temperature of the cooling gas atentry into the pressure shell may be e.g. about 100° C.

In the reactor system 100 shown in FIGS. 1a to 2, inert material (notshown in FIGS. 1a -2) is advantageously present between the lower sideof the structured catalyst 10 and the bottom of the pressure shell.Moreover, inert material is advantageously present between the outersides of the structured catalyst 10 of macroscopic structures 5 and theinsulating material 30. Thus, one side of the insulating material 30faces the inner side of the pressure shell 20 and the other side of theinsulating material 30 faces the inert material. The inert materiel ise.g. ceramic material and may be in the form of pellets. The inertmaterial assists in controlling the pressure drop across the reactorsystem 100 and in controlling the flow of the gas through the reactorsystem 100, so that the gas flows over the surfaces of the structuredcatalyst 10.

FIGS. 3a and 3b show schematic cross sections through an embodiment ofthe inventive reactor system 100′, 100″ comprising a structured catalyst10 a. The structured catalyst 10 a may consist of a single macroscopicstructure with ceramic coating supporting catalytically active materialor it may contain two or more macroscopic structures. Each of thereactor systems 100′, 100″ comprises a pressure shell 20 and a heatinsulation layer 80 between the structured catalyst 10 a and thepressure shell 20. In FIGS. 3a and 3b , the inert material 90 isindicated by hatching. Inert material 90 can be used to fill the gapbetween the structured catalyst 10 a and the heat insulation layer orthe pressure shell 20. In FIGS. 3a and 3b , the inert material 90 isindicated by dotted area; the inert material 90 may be in anyappropriate form, e.g. in the form of inert pellets, and it is e.g. ofceramic material. The inert material 90 assists in controlling thepressure drop through the reactor system and in controlling the flow ofthe gas through the reactor system. Moreover, the inert materialtypically has a heat insulating effect.

From FIGS. 3a and 3b it is seen that the reactor systems 100′, 100″further comprise an inner tube 15 in heat exchange relationship with thestructured catalyst 10 a. The inner tube 15 is adapted to withdraw aproduct gas from the structured catalyst 10 a so that the product gasflowing through the inner tube or tubes is in heat exchange relationshipwith the gas flowing through the structured catalyst; however, the innertube 15 is electrically insulated from the structured catalyst 10 a byeither heat insulation 80, inert material 90, a gap, or a combination.This is a layout which is denoted a bayonet reactor system. In thislayout the product gas within the inner tube assists in heating theprocess gas flowing over the macroscopic structure. In the layouts shownin FIGS. 3a and 3b , the feed gas enters the reactor system 100′, 100″through an inlet as indicated by the arrow 11, and enters into thestructured catalyst 10 a at a first end 101 a thereof, as indicated bythe arrows 13. During the passage of the feed gas through the structuredcatalyst 10 a, it undergoes the steam reforming reaction. The gasexiting from a second end 102 a of the structured catalyst 10 a is atleast partly reformed. The at least partly reformed gas flows exitingfrom the second end 102 a of the structured catalyst 10 a enters intothe inner tube 15 as indicated by the arrows 14, and exits the innertube through an outlet of the pressure shell, as indicated by the arrows12. Even though the inert material 80 is present between the inner tube15 and the structured catalyst 10 a, some heat transfer will take placefrom the gas within the inner tube 15 and the gas within the structuredcatalyst 10 a or upstream the structured catalyst 10 a. In theembodiments shown in FIGS. 3a and 3b , the feed gas flow downwardsthrough the structured catalyst 10 a, from a first end 101 a of thestructured catalyst towards a second end 102 a thereof, and subsequentlyupwards through the inner tube 15; however, it is conceivable that theconfiguration was turned upside-down so that the feed gas would flowupwards through the structured catalyst 10 a and downwards through theinner tube 15. In this case, the lower end of the structured catalystwould be the first end, and the upper end of the structured catalystwould be the second end.

FIGS. 4 and 5 show an embodiment of a structured catalyst comprising anarray of macroscopic structures as seen from above and from the side,respectively. FIG. 4 shows a structured catalyst 10 comprising an arrayof macroscopic structure 5 seen from above, viz. as seen from the arrow11 in FIGS. 1a and 1b . The array has 6 rows, viz. 1 a, 1 b, 1 c, 1 d, 1e, and 1 f, of five macroscopic structures 5. The macroscopic structures5 in each row are connected to its neighboring macroscopic structure (s)in the same row and the two outermost macroscopic structures in each roware connected to a conductor contact rail 41. The neighboringmacroscopic structure 5 in a row of macroscopic structures are connectedto each other by means of a connection piece 3.

FIG. 5 shows the structured catalyst 10 having an array of macroscopicstructures 5 of FIG. 4 seen from the side. From FIG. 5, it can be seenthat each macroscopic structure 5 extends longitudinally perpendicularto the cross section seen in FIG. 4. Each macroscopic structure 5 has aslit 60 cut into it along its longitudinal direction (see FIG. 5).Therefore, when energized by the power source, the current enters thearray of macroscopic structures 5 via a conductor contact rail 41, isled through the first macroscopic structure 5 downwards until the lowerlimit of the slit 60 and is subsequently led upwards towards aconnection piece 3. The current is led via a corresponding zigzag path,downwards and upwards, through each macroscopic structure 5 in each row1 a-1 f of macroscopic structures 5 in the array 10. This configurationadvantageously increases the resistance over the structured catalyst 10.

FIG. 6 shows a structured catalyst 10′ according to the invention in aperspective view. The structured catalyst 10′ comprises a macroscopicstructure that is coated with a ceramic coating impregnated withcatalytically active material. Within the structured catalyst arechannels 70 extending along the longitudinal direction (shown by thearrow indicate ‘h’ in FIG. 6) of the macroscopic structure 5; thechannels are defined by walls 75. In the embodiment shown in FIG. 6, thewalls 75 define a number of parallel, square channels 70 when seen fromthe direction of flow as indicated by the arrow 12. The structuredcatalyst 10′ has a substantially square perimeter when seen from above,defined by the edge lengths e1 and e2. However, the perimeter could alsobe circular or another shape.

The walls 75 of the structured catalyst 10′ are of extruded materialcoated with a ceramic coating, e.g. an oxide, which has been coated ontothe macroscopic structure. In the Figures, the ceramic coating is notshown. The ceramic coating is impregnated with catalytically activematerial. The ceramic coating and thus the catalytically active materialare present on every walls within the structured catalyst 10′ over whichthe gas flow flows during operation and interacts with the heatedsurface of the structured catalyst and the catalytically activematerial.

Thus, during use in a reactor system for steam reforming, a hydrocarbonfeed gas flows through the channels 70 and interacts with the heatedsurface of the structured catalyst and with the catalytically activematerial supported by the ceramic coating.

In the structured catalyst 10′ shown in FIG. 6 a slit 60 has been cutinto the structured catalyst 10′. This slit 60 forces a current to takea zigzag route, in this instance downwards and subsequently upwards,within the macroscopic structure thereby increasing the current path andthus the resistance and consequently the heat dissipated within themacroscopic structure. The slit 60 within the macroscopic structure maybe provided with embedded insulating material in order to ensure that nocurrent flows in the transverse direction of the slit 60.

The channels 70 in the structured catalyst 5 are open in both ends. Inuse of the structured catalyst in a reactor system, a hydrocarbon feedgas flows through the unit, in the direction shown by arrows 11 and 12in FIGS. 1a and 1b , and gets heated via contact with the walls 75 ofthe channels 70 and by heat radiation. The heat initiates the desiredsteam reforming process. The walls 75 of the channels 70 may e.g. have athickness of 0.5 mm, and the ceramic coating coated onto the walls 75may e.g. have a thickness of 0.1 mm. Even though the arrows 11 and 12(see FIGS. 1a and 1b ) indicate that the flow of the hydrocarbon feedgas is down-flow, the opposite flow direction, viz. an up-flow, is alsoconceivable.

FIG. 7 shows the structured catalyst 5 of FIGS. 1a and 1b in aperspective view and with connectors 7 attached. The connectors 7 eachconnects a part of the structured catalyst 10′ to a conductor 40. Theconductors 40 are both connected to a power supply (not shown). Each ofthe connectors 7 are connected to an upper part of the structuredcatalyst. When the conductors 40 are connected to a power supply, anelectrical current is led to the corresponding connector 7 via theconductor and runs through the structured catalyst 10′. The slit 60hinders the current flow in a transverse direction (horizontal directionof FIG. 7) throughout its lengths along the height h of the structuredcatalyst 10′. Therefore, the current runs in a direction downwards asseen in FIG. 7 in the part of the structured catalyst along the slit 60,subsequently it runs transversely to the longitudinal direction belowthe slit 60 as seen in FIG. 7 and finally the current runs upwards inthe longitudinal direction of the structured catalyst to the otherconnector 7. The connectors 7 in FIG. 7 are mechanically fastened to thestructured catalyst by means of i.a. mechanical fastening means such asscrews and bolts. However, additional or alternative fastening means areconceivable. In an embodiment, the electrical power supply generates avoltage of 3V and a current of 400 A.

The connectors 7 are e.g. made in materials like iron, aluminum, nickel,copper, or alloys thereof.

As mentioned, the structured catalyst 10′ is coated with a ceramiccoating, such as an oxide, supporting the catalytically active material.However, the parts of the structured catalyst 10′ which are connected tothe connectors 7 should not be coated with an oxide. Instead, themacroscopic structure of the structured catalyst should be exposed orconnected directly to the connectors 7 in order to obtain a goodelectrical connection between the macroscopic structure and theconnector.

When the connectors 7 and thus the conductors 40 are connected to thesame end of the structured catalyst 5, viz. the upper end as seen inFIG. 7, the gas entering into a reactor system housing the structuredcatalyst 10′ would be able to cool the connectors 7 and the conductors40. For instance, the hydrocarbon gas entering into such a reactorsystem would have a temperature of 400° C. or 500° C. and would thuskeep the connectors 7 and conductors 40 from reaching temperatures muchhigher than this temperature.

FIG. 8 shows another embodiment of a structured catalyst 10′ withconnectors 7′″. The structured catalyst 10′ is e.g. the structuredcatalyst as shown in FIG. 6. Each of the connectors 7′″ has three holesat an upper side thereof for connection to conductors (not shown). Apiece of electrically insulating material 61 is inside the slit 60 (seeFIG. 6) of the structured catalyst 10′.

FIG. 9a shows an embodiment of a structured catalyst 10″ for use in thereactor system of the invention. FIG. 9a shows the structured catalyst10″ in a perspective view. It can be seen that the structured catalyst10″ has a single vertical slit 60 along the longitudinal axis of thecatalyst 10″ as shown in FIG. 9a . The single vertical slit 60 extendsfrom the top of the structured catalyst 10″ towards the bottom thereof,along about 90% of the length of the structured catalyst. The singlevertical slit 60 can be seen as parting the structured catalyst 10″ intotwo halves. Each of these two halves has five horizontal slits 65. Thevertical slit 60 and the horizontal slits 65 function to direct thecurrent in a zig-zag route through the structured catalyst.

FIG. 9b shows the current density of the structured catalyst 10″ shownin FIG. 9a as a function of the electrical effect transferred to thestructured catalyst 10″. FIG. 9b is the result of a multiphysicscomputational fluid dynamics simulations in Comsol software of thecurrent distribution of the structure in FIG. 9a . In FIG. 9b thestructured catalyst 10″ is seen from the side. Two conductors (not shownin FIG. 9b ) are connected to the upper end on the left side of thestructured catalyst 10″. As illustrated by the intensity of the currentdensity, as depicted on the scale in the right part of FIG. 9b , when apower source is connected to the structured catalyst 10″, a current runsfrom the upper end thereof in zig-zag form, due to the horizontal slits,to the bottom of the structure catalyst 10″, to the back thereof, viz.into the paper as seen in FIG. 9b , and subsequently upwards in zig-zagform towards the second conductor. The temperature of the structuredcatalyst 10″ depends upon the current density throughout the structuredcatalyst 10″. It can be seen in FIG. 9b , that the current density ishighest at the end points of horizontal slits 65 into the structuredcatalyst 10″. These points are the points where the current path turnsdirection, i.e. where the current through the structured catalyst 10″ isforced or directed in another direction. Moreover, it can be deducedthat the current density vector of the principal current path has anon-zero component value parallel to the length of said structuredcatalyst for more than 80% of the structure. In conclusion, it is clearfrom FIG. 9b that the principal current path can be controlled in thestructured catalyst. This feature gives control of the temperatureprofile inside the structured catalyst.

FIG. 10 a schematic drawing of a cross-section through structuredcatalyst with electrically insulating parts. FIG. 10 is a schematicdrawing of a cross-section through a structured catalyst 10′″ of theinvention, with electrically insulating parts 61′. The electricallyinsulating parts are shown as hatched parts in FIG. 10. In theembodiment shown in FIG. 10, three pieces of electrically insulatingparts 61′ intersects the structured catalyst 10′″ in most of thelongitudinal direction thereof. Conductors 7 are connected to the upperside of the structured catalyst 10′″ as seen in FIG. 10. During use ofthe structured catalyst 10′″, the conductors 7 are connected to a powersupply and a hydrocarbon feed gas is brought into contact with thestructured catalyst 10″′. Thus, current runs from the first conductorthrough the structured catalyst 10′″ in a zigzag direction, viz.downwards from the first conductor and around the lower side of thefirst electrically insulating part 61′, subsequently upwards and aroundthe upper side of the middle electrically insulating part 61′, thendownwards again and around the lower side of the third electricallyinsulating part 61′ and finally upwards to the second conductor 7. Itshould be noted that any appropriate number of electrically insulatingparts 61′ is conceivable. The electrically insulating parts 61′ aresolid, electrically insulating material, e.g. glass, and they areprovided in cuts or slits in the macroscopic structure. The electricallyinsulating parts 61′ ensures that the parts of the macroscopic structureon the sides electrically insulating parts 61′ are kept from each other.It should be noted, that in this embodiment, as in all the embodimentsof the invention, the direction of flow of gas may be the same as thedirection of the current through the structured catalyst, or it may bedifferent. In the embodiment of FIG. 10, the direction of flow of gas ise.g. from the upper side of the structured catalyst 10′″ towards thebottom of the structured catalyst 10′″; thus, the flow of current onlythe same as the direction of the flow of gas as some parts of thestructured catalyst 10′″, whilst the direction of the current istransverse to the direction of the flow of gas at some parts andopposite (upwards) in some parts.

FIGS. 11a and 11b shows temperature and conversion profiles as afunction of electrical effect transferred to the structured catalyst.FIG. 11a is the result of a laboratory test of bench scale reactorsystem having a length of 12 cm and a volume 108 cm³ of the structuredcatalyst as defined by the outer walls/sides thereof and configurationas depicted in FIG. 6 where Cu conductors has been welded to the first 2cm of the monolith on opposing sides in the first end. The pressure ofthe pressure shell was 3.5 bar, the temperature of the feed gas inletinto the reactor system was about 200° C. The composition of the feedgas was 31.8% CH₄, 2.4% H₂, 65.8% H₂O and the total gas flow was 102.2NI/h. It should be noted, that the energy balance is substantiallybetter in a larger scale than in the small scale experimental conditionsbehind the graphs of FIG. 11a , due to high energy loss in this relativesmall scale. However, it is clear from FIG. 11a that with increasingpower, both the conversion of methane and the temperature increases. Thetemperature reaches above 900° C. and the methane convercion reachesabove 98%.

FIG. 11b shows a similar experiment as described above, but with apressure of 21 bar. Again, it is clear from FIG. 11b that withincreasing power, both the conversion of methane and the temperatureincreases. The temperature reaches above 1060° C. and the methaneconversion reaches above 95%.

FIGS. 12a and 12b show simulation results for temperatures and gascomposition along the length of structured catalyst. A single channel ofa structured catalyst is simulated. The length of the structuredcatalyst of this simulation, and thus of the single channel, is 10 cm.The conditions within the pressure shell/structured catalyst/channel is:

-   -   Pressure: 29 barg    -   T inlet: 466° C.    -   Total flow: 30 NI/h    -   Composition of the feed gas inlet into the reactor/channel:        31.8% methane,    -   8.8% hydrogen, 2.3% carbon dioxide, and 57.1% steam.

In FIG. 12a , the temperature of the wall of the channel is indicated byTw and the temperature in the center of the channel is indicated by Tc.Tw and Tc are read from the scale to the right of the graphs. Themethane conversion is indicated by Cc and is read from the scale to theleft of the graphs.

From FIG. 12a it is seen that the temperature of the wall of a channelin the structured catalyst increases continuously along almost all ofthe length of the structured catalyst. The temperature is about 480° C.at the first end of the structured catalyst (z=0 cm) and about 1020° C.at the second end of the structured catalyst (z=10 cm). The increase oftemperature is steepest the first 10% of the structured catalyst, andonly in the last few percent of the length of the structured catalyst,the temperature does not change much. Thus, when the current turnsaround at the second end of the structured catalyst, from goingdownwards to upwards in the FIGS. 1-9 a, the temperature of the walls ofthe channels of the structured catalyst does not change substantiallyfor increasing z-values. However, FIG. 12a also shows that thetemperature in the center of the channel keeps on increasing along thewhole length of the structured catalyst. It should be noted, though,that the temperature in the center of the channel remains substantiallyconstant for the first 5-7% of the length of the structured catalyst.This is due to the fact that the gas inlet into the structured catalystcools the structured catalyst in the vicinity of the first end thereofand due to thermal energy transport delay from the wall to the center ofthe channel.

In FIG. 12a , the conversion of methane in the center of the channel ofthe structured catalyst is also shown. It can be seen that theconversion is close to zero for the first 10-12% of the length of thechannel, and that the conversion subsequently increases monotonously andreaches a value of about 85%. As noted above, small scale reactors andsimulations thereof provide for less than optimal numbers, and thatconsiderably higher conversion is achievable in a real scale reactorsystem. However, the simulation provides information on the tendenciesof the conversion rate and temperature throughout the structuredcatalyst.

FIG. 12b shows the partial pressures of the principle active gasseswithin the channel of the structured catalyst of FIG. 12a . From FIG.12b it is clear that the partial pressures of steam and methane diminishconsiderably along the length of the channel of the structured catalyst,whilst the partial pressures of hydrogen and carbon monoxide increaseconsiderably. Moreover, the partial pressure of carbon dioxide increasesslightly along the length of the structured catalyst, but decreasestowards the highest temperatures where the reverse water gas shiftreaction is thermodynamically favored.

FIG. 13 shows the required maximum temperature within the reactor systemof the invention as a function of the pressure for pressures of about 30bar to about 170 bar during steam reforming of a feed gas consisting of30.08% CH₄, 69.18% H₂O, 0.09% H₂, 0.45% CO₂, 0.03% Ar, 0.02% CO, 0.15%N₂ to a methane conversion of 88% at a 10° C. approach to the steammethane reforming equilibrium. The required maximum temperatureincreases with pressure due to Le Chatelier's principle. This shows thatthe high temperatures which can be used in the current invention allowsfor using pressures which are significantly higher than the pressuresused in a traditional SMR, where the external heating of the tubesprohibit the temperature exceeding ca. 950° C. A temperature of 950° C.corresponds to 27 barg in FIG. 13. In a reactor system of the invention,a maximum temperature of e.g. 1150° C. can be used which allows for apressure of up to 146 barg with the same conversion of methane asindicated above.

FIG. 14 is a graph of the approach to equilibrium (ΔT_(app,SMR)) of thesteam methane reforming reaction for different gas flow rates throughthe structured catalyst. FIG. 14 shows that for a given gas flow ratethrough the structured catalyst, the approach to equilibrium at theentry into a reactor system housing the structured catalyst, is in therange 160-175° C., because the feed gas is far from equilibrium. Whenthe hydrocarbon gas flows through the structured catalyst, the approachto equilibrium is reduced due to the catalytic reactions. FIG. 14 showsthe approach to equilibrium (ΔT_(app,SMR)) for gas flow rates from 10000Nm³/h to 200000 Nm³/h. For the lowest gas flow rate, 10000 Nm³/h, theapproach to equilibrium becomes less than 10° C. at about 13% of thereactor system length. Here, the reactor system length is seen as outerheight of the structured catalyst in the direction of the flow, so thatthe reactor system length of the structured catalyst 10 is about 1 h inthe embodiment of FIG. 6. For higher gas flow rates, the approach toequilibrium is higher the higher the gas flow rate, so that for a gasflow rate of 200000 Nm³/h, the approach to equilibrium reaches a minimumvalue just below 80° C.

A general trend in all the curves in the FIG. 14 is that the approach toequilibrium is continuously decreasing from the entry into thestructured catalyst until a pseudo equilibrium is reached, where theheat added and the heat consumed roughly equal each other. The approachto equilibrium from this stage is substantially constant or has aslightly increasing development due to the overall increasingtemperature of the reactor system. For e.g. the flow rate 150 000 Nm³/h,the approach to equilibrium goes below 60° C. at about 80% of thereactor system length, but subsequently increases to about 60° C.

It should be noted, that even though the structured catalysts shown inthe figures are shown as having channels with a square cross section, asseen perpendicular to the z axis, any appropriate shape of the crosssections of the channels is conceivable. Thus, the channels of thestructured catalyst could alternatively be e.g. triangular, hexagonal,octagonal, or circular, where triangular, square, and hexagonal shapesare preferred.

EXAMPLES

While the invention has been illustrated by a description of variousembodiments and examples while these embodiments and examples have beendescribed in considerable detail, it is not the intention of theapplicant to restrict or in any way limit the scope of the appendedclaims to such detail. Additional advantages and modifications willreadily appear to those skilled in the art. The invention in its broaderaspects is therefore not limited to the specific details, representativemethods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicant's general inventive concept.

All the examples described below relate to compact reactor systems. Thisis possible due to the reactor systems comprise compact structuredcatalysts in the form of compact macroscopic supports having a highthermal flux when powered by a power source. It is moreover to be noted,that the dimensions of the structured catalysts may be chosen relativelyfreely, so that the structured catalyst may be almost cubic in outershape or it may be wider than its height.

The examples all describe operation conditions with high pressure,ranging from 28 bar to 182 bar. Such high pressures are made possible bythe configuration of the reactor system since the structured catalystwithin the reactor system has high thermal flux upon powering by a powersource, is to some extent thermally insulated from the pressure shell,and the pressure drop through the structured catalyst is very lowcompared to an SMR. The structured catalyst will obtain the highesttemperature within the reactor system, while the pressure shell willhave a significantly lower temperature due to the thermal insulationbetween the structured catalyst and the pressure shell. Ideally, thetemperature of the pressure shell will not exceed 500° C. When productgas with a high pressure is needed, such as 30 bar or above, the productgas exiting the reactor system can in many cases be used directly,without the use of compressors. This is due to the possibility ofpressurizing the feed gas upstream the reactor system of the invention.Pressurizing the feed gas will require less energy than the product gasas the volume of the feed is lower than the product gas as the steamreforming reaction has a net production of molecules. Additionally, oneof the feed gas constituents may be pumped which requires significantlyless energy compared to gas compression.

In all the examples described below, the feed gas enters the reactorsystem and flows through the structured catalyst housed therein. Whenthe heat insulation layer of the reactor system is a heat insulatingmaterial, the heat insulating material typically makes up most of thespace between the structured catalyst and the pressure shell along thewalls of the pressure shell so that the feed gas is forced to flow alongwalls of the macroscopic structure on its way through the pressureshell.

The examples below (except for the comparative example) all relate to areactor system with a structured catalyst. The structured catalystsdescribed in these examples comprise one or more macroscopic structures.The one or more macroscopic structures of the examples below all supporta ceramic coating supporting catalytically active material.Advantageously, substantially all the surface of the macroscopicstructure supports the ceramic coating supporting the catalyticallyactive material; however, at connections points, e.g. between twoadjacent macroscopic structures or between a macroscopic structure and aconductor, the macroscopic structure may be free from ceramic coating inorder to facilitate connection between a conductor and the macroscopicstructure.

Example 1

An example calculation of the process of the invention is given in Table1 below. A feed gas is fed to the reactor system of the invention. Thefeed gas entering the reactor system is pressurized to a pressure of 28kg/cm²·g and has a temperature of 500° C. Inside the reactor system, astructured catalyst with nine macroscopic structures having a squarecross section are placed in an array and each macroscopic structure hasa size of 0.53 times 0.53 times 2.3 meter. Each macroscopic structureadditionally has 17778 channels with a square cross section having aside or edge length of 0.32 cm. Each macroscopic structure has slitsparallel to the longitudinal direction thereof, so that clusters of 5times 5 channels are formed. The clusters are individually insulatedfrom the neighboring cluster, except from the ends, so that the currentpath through the macroscopic structure is a zigzag path. A current of200 A and a voltage of ca. 5.5 kV are applied to each macroscopicstructure in the reactor system of the invention in order to heat thestructured catalyst and thus the gas passing through the structuredcatalyst, corresponding to a power supplied in the structured catalystsof 9899 kW.

The reactor system in the current configuration could have an overallinternal diameter of the reactor system of 3.2 m and a total internalheight of 5.5 m when the reactor system is made as a cylindrical reactorsystem with spherical heads. In this specific configuration, themacroscopic structures are placed in a square orientation having adiagonal length of 2.3 m. In all the examples described herein, exceptfor the comparative example, inert material is placed around thestructured catalyst to close the gap to the insulation material,adjacent to the pressure shell. The insulation material in example 1 hasa cylindrical form with an internal diameter of 2.5 m and a thickness of0.35 m.

During the passage of the feed gas through the reactor system, the feedgas is heated by the structured catalyst and undergoes steam reformingto a product gas having an exit temperature of 963° C.

TABLE 1 Size of macroscopic structure: Edge size [m] 0.53 Height [m]2.3  Number of macroscopic structures 9   Total volume of structuredcatalyst [L] 5888     Structured catalyst height/diagonal length [—]1.02 Feed gas Product gas T [° C.] 500 963 P [kg/cm² g] 27.97 27.47 CO2[Nm³/h] 168 727 N2 [Nm³/h] 26 26 CH4 [Nm³/h] 2630 164 H2 [Nm³/h] 5908545 CO [Nm³/h] 1 1907 H2O [Nm³/h] 8046 5022 Total flow [Nm³/h] 1146116391 ΔT_(app, SMR) [° C.] 10 Power [kW] 9899     Heat flux [kW/m²] 2.2 Space velocity [Nm³/m³/h] 1950    

Example 2

An example calculation of the process of the invention is given in Table2 below. A feed gas is fed to the reactor system of the invention. Thefeed gas entering the reactor system is pressurized to a pressure of 28kg/cm²·g and has a temperature of 500° C. Inside the reactor system, astructured catalyst in the form of 1 macroscopic structure having asquare cross section is placed which has a size of 0.4 times 0.4 times0.35 meter. The macroscopic structure additionally has 10000 channelswith a square cross section having a side or edge length of 0.32 cm. Themacroscopic structure has slits parallel to the longitudinal directionthereof, so that clusters of 5 times 5 channels are formed. The clustersare individually insulated from the neighboring cluster, except from theends, so that the current path through the macroscopic structure is azigzag path. A current of 200 A and a voltage of ca. 500 V are appliedto the macroscopic structure in the reactor system of the invention inorder to heat the structured catalyst and thus the gas passing throughthe structured catalyst, corresponding to a power deposited in thestructured catalyst of 99 kW.

The reactor system in the current configuration could have an overallinternal diameter of the reactor system of 1.2 m and a total internalheight of 1.5 m when the reactor system is made as a cylindrical reactorsystem with spherical heads. In this specific configuration, thestructured catalyst has a diagonal length of 0.6 m. Inert material isplaced around the structured catalysts to close the gap to theinsulation material which has an internal diameter of 0.6 m and athickness of 0.3 m.

During the passage of the feed gas through the reactor system, the feedgas is heated by the structured catalyst and undergoes steam reformingto a product gas having an exit temperature of 963° C.

TABLE 2 Size of macroscopic structure: Edge size [m] 0.4 Height [m] 0.35 Number of macroscopic structures 1   Total volume of structuredcatalyst [L] 55.4  Structured catalyst height/diagonal length [—]  0.61Feed gas Product gas T [° C.] 500 963 P [kg/cm² g] 27.97 27.47 CO2[Nm³/h] 1.7 7.3 N2 [Nm³/h] 0.3 0.3 CH4 [Nm³/h] 26.3 1.6 H2 [Nm³/h] 5.985.4 CO [Nm³/h] 0 19.1 H2O [Nm³/h] 80.5 50.2 Total flow [Nm³/h] 114.7163.9 ΔT_(app, SMR) [° C.] 10 Power [kW] 99   Heat flux [kW/m²] 2.2Space velocity [Nm³/m³/h] 2071   

Example 3

An example calculation of the process of the invention is given in Table3 below. A feed gas is fed to the reactor system of the invention. Thefeed gas entering the reactor system is pressurized to a pressure of 97bar, viz. 97 kg/cm²·g and has a temperature of 500° C.

Inside the reactor system, a structured catalyst comprising ninemacroscopic structures having a square cross section are placed in anarray and each macroscopic structure has a size of 0.53 times 0.53 times2.3 meter. Each macroscopic structure additionally has 17778 channelswith a square cross section having a side or edge length of 0.32 cm.Each macroscopic structure has slits parallel to the longitudinaldirection thereof, so that clusters of 5 times 5 channels are formed.The clusters are individually insulated from the neighboring cluster,except from the ends so that the current path through the macroscopicstructure is a zigzag path. A current of 200 A and a voltage of ca. 5.5kV are applied to each macroscopic structure in the reactor system ofthe invention in order to heat the structured catalyst and thus the gaspassing through the structured catalyst, corresponding to a powerdeposited in the structured catalyst of 9899 kW.

The reactor system in the current configuration could have an overallinternal diameter of the reactor system of 3.2 m and a total internalheight of 5.5 m when the reactor system is made as a cylindrical reactorsystem with spherical heads. In this specific configuration, themacroscopic structures are placed in a square orientation having adiagonal length of 2.3 m. Inert material is placed around the structuredcatalyst to close the gap to the insulation material which has aninternal diameter of 2.5 m and a thickness of 0.35 m.

During the passage of the feed gas through the reactor system, the feedgas is heated by the structured catalyst and undergoes steam reformingto a product gas having an exit temperature of 1115° C. It is seen fromTable 3 that the total flows of the feed gas and the product gas arelower in Example 3 compared to Example 1.

Since the product gas exiting the reactor system is pressurized to apressure of 97 bar, no compressors will be needed downstream the reactorsystem when a high pressure product gas is requested. This reduces theoverall cost of a plant with a reactor system of the invention.

TABLE 3 Size of macroscopic structure: Edge size [m]  0.53 Height [m]2.3 Number of macroscopic structures 9   Total volume of structuredcatalyst [L] 5888    Structured catalyst height/diagonal length [—] 1.01 Feed gas Product gas T [° C.] 500 1115 P [kg/cm² g] 96.97 96.47CO2 [Nm³/h] 111 510 N2 [Nm³/h] 23 23 CH4 [Nm³/h] 2337 143 H2 [Nm³/h] 3727354 CO [Nm³/h] 1 1796 H2O [Nm³/h] 7111 4518 Total flow [Nm³/h] 995514344 ΔT_(app, SMR) [° C.] 10 Power [kW] 9899    Heat flux [kW/m²] 2.2Space velocity [Nm³/m³/h] 1691   

Example 4

An example calculation of the process of the invention is given in Table3 below. A feed gas is fed to the reactor system of the invention. Thefeed gas entering the reactor system is pressurized to a pressure of 28bar, viz. 28 kg/cm²·g and has a temperature of 500° C.

Inside the reactor system, a structured catalyst comprising 25macroscopic structures having a square cross section are placed in anarray and each macroscopic structure has a size of 0.24 times 0.24 times0.9 meter. Each macroscopic structure additionally has 3600 channelswith a square cross section having a side or edge length of 0.33 cm inlength. Each macroscopic structure has slits parallel to thelongitudinal direction thereof, so that clusters of 10 times 10 channelsare formed. The clusters are individually insulated from the neighboringcluster, except from the ends, so that the current path through themacroscopic structure is a zigzag path. A current of 1500 A and avoltage of ca. 260 V are applied to each macroscopic structure in thereactor system of the invention in order to heat the structured catalystand thus the gas passing through the structured catalyst, correspondingto a power deposited in the structured catalyst of 9899 kW.

The reactor system in the current configuration could have an overallinternal diameter of the reactor system of 2.3 m and a total internalheight of 3.2 m when the reactor system is made as a cylindrical reactorsystem with spherical heads. In this specific configuration, themacroscopic structures are placed in a square orientation having adiagonal length of 1.7 m. Inert material is placed around the structuredcatalyst to close the gap to the insulation material which has aninternal diameter of 1.8 m and a thickness of 0.25 m.

During the passage of the feed gas through the reactor system, the feedgas is heated by the structured catalyst and undergoes steam reformingto a product gas having an exit temperature of 963° C. It is seen fromTable 4 that the structured catalyst of Example 4 is somewhat smallerthan the one used in Examples 1 and 3 due to the higher current. Thetotal flows of the feed gas and the product gas correspond to the flowsof Example 1.

TABLE 4 Size of macroscopic structure: Edge size [m]  0.24 Height [m]0.9 Number of macroscopic structures 25   Total volume of structuredcatalyst [L] 1324    Structured catalyst height/diagonal length [—] 0.54 Feed gas Product gas T [° C.] 500 963 P [kg/cm² g] 27.97 27.47 CO2[Nm³/h] 168 727 N2 [Nm³/h] 26 26 CH4 [Nm³/h] 2630 164 H2 [Nm³/h] 5908545 CO [Nm³/h] 1 1907 H2O [Nm³/h] 8046 5022 Total flow [Nm³/h] 1146116391 ΔT_(app, SMR) [° C.] 10 Power [kW] 9899    Heat flux [kW/m²] 9.0Space velocity [Nm³/m³/h] 8653   

Example 5

An example calculation of the process of the invention is given in Table4 below. A feed gas is fed to the reactor system of the invention. Thefeed gas entering the reactor system is pressurized to a pressure of 182bar and has a temperature of 500° C.

Inside the reactor system, a structured catalyst comprising ninemacroscopic structures having a square cross section are placed in anarray and each macroscopic structure has a size of 0.53 times 0.53 times2.3 meter. Each macroscopic structure additionally has 17778 channelswith a square cross section having a side or edge length of 0.32 cm.Each macroscopic structure has slits parallel to the longitudinaldirection thereof, so that clusters of 5 times 5 channels are formed.The clusters are individually insulated from the neighboring cluster,except from the ends, so that the current path through the macroscopicstructure has a zigzag path. A current of 200 A and a voltage of ca. 5.5kV are applied to each macroscopic structure in the reactor system ofthe invention in order to heat the structured catalyst and thus the gaspassing through the structured catalyst, corresponding to a powerdeposited in the structured catalyst of 9899 kW.

The reactor system in the current configuration could have an overallinternal diameter of the reactor system of 3.2 m and a total internalheight of 5.5 m when the reactor system is made as a cylindrical reactorsystem with spherical heads. In this specific configuration, themacroscopic structures are placed in a square orientation having adiagonal length of 2.3 m. Inert material is placed around the structuredcatalyst to close the gap to the insulation material which has aninternal diameter of 2.5 m and a thickness of 0.35 m.

During the passage of the feed gas through the reactor system, the feedgas is heated by the structured catalyst and undergoes steam reformingto a product gas having an exit temperature of 1236° C. The total flowsof the feed gas and the product gas are lower than the total flows ofthe gasses in Examples 1 and 4.

Since the product gas exiting the reactor system is already pressurizedto a pressure of 181 bar, it is suited for being input into e.g. ahydrotreater of a refinery plant without further pressurizing. Thus, nocompressors will be needed between the reactor system and thehydrotreater of the refinery plant. This reduces the overall cost of theplant with a reactor system of the invention.

TABLE 5 Size of macroscopic structure: Edge size [m]  0.53 Height [m]2.3 Number of macroscopic structures 9   Total volume of structuredcatalyst [L] 5888    Structured catalyst height/diagonal length [—] 1.01 Feed gas Product gas T [° C.] 500 1236 P [kg/cm² g] 181.97 181.47CO2 [Nm³/h] 86 395 N2 [Nm³/h] 21 21 CH4 [Nm³/h] 2116 96 H2 [Nm³/h] 2786648 CO [Nm³/h] 0 1711 H2O [Nm³/h] 6425 4096 Total flow [Nm³/h] 892612967 ΔT_(app, SMR) [° C.] 10 Power [kW] 9899    Heat flux [kW/m²] 2.2Space velocity [Nm³/m³/h] 1516   

Example 6

Example 6 relates to a reactor system comprising a structured catalystin the form of a structured catalyst having in total 78540 channels witha total wall length of one channel in the cross section of 0.00628 meach and a length of 2 m, giving a total surface area of 987 m² ofcatalyst surface. For a reactor system with this structured catalyst, asimulation with varying gas flow through the structured catalyst wasmade where the gas composition in all calculations was 8.8% H₂, 56.8%H₂O, 0.2% N₂, 0.1% CO, 2.3% CO₂, and 31.8% CH₄. In each simulation akinetic model for steam reforming and water gas shift was used and avariation in the surface flux (Q) of energy from the electrically heatedstructured catalyst was made to adjust the exit temperature of theproduct gas from the reactor system housing the structured catalyst to920° C. The kinetic model used was similar to the approach used by Xuand Froment, (J. Xu and G. F. Froment, Methane steam reforming,methanation and water-gas shift: I. intrinsic kinetics. AmericanInstitution of Chemical Engineers Journal, 35:88-96, 1989.). FIG. 14shows the approach to equilibrium along the reactor system length atvarying total flows. The Figure shows that at low feed flows (10000Nm³/h), the approach to the equilibrium at the outlet the reactor systemis below 5° C., which translate into a hydrocarbon conversion of 77%,while at the high flows (150000 Nm³/h) the approach to equilibrium isabove 60° C., which correspond to a hydrocarbon conversion of only 64%,and the hydrocarbons therefore are used less efficiently. The closecontrol of the heat flux in the current invention therefore allows forcontrolling the approach to equilibrium closely along the length of thereactor system. A general trend in all the curves in FIG. 14 is that theapproach to equilibrium is continuously decreasing until a pseudoequilibrium is reached, where the heat added and the heat consumedroughly equal each other.

The approach to equilibrium from this stage is substantially constant orhas a slightly increasing development due to the overall increasingtemperature of the reactor system.

Example 7 (Comparative Example)

An SMR with a number of identical tubes is provided. Each tube has aninternal diameter of 10 cm and a length of 13 m. The total heat flux tothe SMR tubes is adjusted to an average heat flux (based on the surfacearea of the inner surface of the tubes) of 90,000 kcal/h/m²corresponding to ca. 105 kW/m². Each tube is loaded with catalystpellets. The dimensions of the catalyst pellets are adjusted to give avoid fraction of 60%. Such a configuration allows for processing around410 Nm³/h of process gas per tube in the SMR, when the feed gas has acomposition of 8.8% hydrogen, 56.8% water, 0.2% nitrogen, 0.1% carbonmonoxide, 2.3% carbon dioxide, and 31.8% methane.

This gives:

-   -   Total internal tube volume (volume limited by the interior        surface of the tube and the height of the tube): 0.1021 m³    -   Internal tube volume occupied by catalyst material: 0.0408 m³    -   Total amount of internal tube volume occupied by catalyst        material per unit of internal reactor system volume: 0.4 m³/m³    -   Total amount of energy supplied to the tube interior: 427.4 kW    -   Amount of energy supplied to the tube interior per unit of tube        interior volume: 4186 kW/m³.    -   Gas processed per reactor catalyst volume: 4015 Nm³/m³/h.

Example 8

A reactor system according to the invention is provided. A structuredcatalyst with a geometric surface area of 800 m²/m³ is provided. 95% ofthe area is covered with a ceramic coating with catalytically activematerial. The ceramic coating has a thickness of 0.1 mm. A power of 9kW/m² of surface area of the structured catalyst is applied. Such areactor can process ca. 7700 Nm³/m³/h relative to the volume of thestructured catalyst, when the feed gas has a composition of 8.8%hydrogen, 56.8% water, 0.2% nitrogen, 0.1% carbon monoxide, 2.3% carbondioxide, and 31.8% methane.

This gives:

-   -   Amount of energy supplied to the structured catalyst per unit of        structured catalyst volume: 7200 kW/m³.    -   Total amount of internal reactor system volume occupied by        catalyst per unit of internal reactor system volume: 0.076        m³/m³.    -   Gas processed per reactor catalyst volume: 101315 Nm³/m³/h

It is seen by comparing with Example 7, that the internal reactor systemvolume can be made much more compact. In addition, in the reactor systemaccording to the invention, no furnace is needed thus substantiallyreducing the reactor size.

Furthermore, the amount of catalytically active material is reducedconsiderably compared to the state of the art.

1. A reactor system for carrying out steam reforming of a feed gascomprising hydrocarbons, said reactor system comprising: a structuredcatalyst arranged for catalyzing steam reforming of said feed gascomprising hydrocarbons, said structured catalyst comprising amacroscopic structure of electrically conductive material, saidmacroscopic structure supporting a ceramic coating, wherein said ceramiccoating supports a catalytically active material; a pressure shellhousing said structured catalyst, said pressure shell comprising aninlet for letting in said feed gas and an outlet for letting out productgas, wherein said inlet is positioned so that said feed gas enters saidstructured catalyst in a first end of said structured catalyst and saidproduct gas exits said structured catalyst from a second end of saidstructured catalyst; a heat insulation layer between said structuredcatalyst and said pressure shell; and at least two conductorselectrically connected to said structured catalyst and to an electricalpower supply placed outside said pressure shell, wherein said electricalpower supply is dimensioned to heat at least part of said structuredcatalyst to a temperature of at least 500° C. by passing an electricalcurrent through said macroscopic structure, wherein said at least twoconductors are connected to the structured catalyst at a position on thestructured catalyst closer to said first end of said structured catalystthan to said second end of said structured catalyst, and wherein thestructured catalyst is constructed to direct an electrical current torun from one conductor substantially to the second end of the structuredcatalyst and return to a second of said at least two conductors.
 2. Areactor system according to claim 1, wherein the pressure shell has adesign pressure of between 5 and 30 bar.
 3. A reactor system accordingto claim 1, wherein the pressure shell has a design pressure of between30 and 200 bar.
 4. A reactor system according to claim 1, wherein theresistivity of the macroscopic structure is between 10⁻⁵ Ω·m and 10⁻⁷Ω·m.
 5. A reactor system according to claim 1, where each of the atleast two conductors are led through the pressure shell in a fitting sothat the at least two conductors are electrically insulated from thepressure shell.
 6. A reactor system according to claim 5, wherein saidpressure shell further comprises one or more inlets close to or incombination with at least one fitting in order to allow a cooling gas toflow over, around, close to, or inside at least one conductor withinsaid pressure shell.
 7. A reactor system according to claim 1, whereinthe reactor system further comprises an inner tube in heat exchangerelationship with but electrically insulated from the structuredcatalyst, said inner tube being adapted to withdraw a product gas fromthe structured catalyst so that the product gas flowing through theinner tube is in heat exchange relationship with gas flowing through thestructured catalyst.
 8. A reactor system according to claim 1, whereinthe connection between the structured catalyst and said at least twoconductors is a mechanical connection, a welded connection, a brazedconnection or a combination thereof.
 9. A reactor system according toclaim 1, wherein the macroscopic structure is an extruded and sinteredstructure or a 3D printed and sintered structure.
 10. A reactor systemaccording to claim 1, wherein the structured catalyst comprises an arrayof macroscopic structures electrically connected to each other.
 11. Areactor system according to claim 1, wherein said structured catalysthas electrically insulating parts arranged to increase the length of aprincipal current path between said at least two conductors to a lengthlarger than the largest dimension of the structured catalyst.
 12. Areactor system according to claim 1, wherein said structured catalysthas at least one electrically insulating part arranged to direct acurrent through said structured catalyst in order to ensure that for atleast 70% of the length of said structured catalyst, a current densityvector of the principal current path has a non-zero component valueparallel to the length of said structured catalyst.
 13. A reactor systemaccording to claim 1, wherein said macroscopic structure has a pluralityof parallel channels, a plurality of non-parallel channels and/or aplurality of labyrinthic channels.
 14. A reactor system according toclaim 1, wherein the reactor system further comprises a bed of a secondcatalyst material upstream said structured catalyst within said pressureshell.
 15. A reactor system according to claim 12, wherein said reactorsystem further comprises a third catalyst material in the form ofcatalyst pellets, extrudates or granulates loaded into the channels ofsaid structured catalyst.
 16. A reactor system according to claim 1,further comprising a bed of fourth catalyst material placed within thepressure shell and downstream the structured catalyst.
 17. A reactorsystem according to claim 1, wherein the material of the macroscopicstructure is chosen as a material arranged to generate a heat flux of500 to 50000 W/m² by resistance heating of the material.
 18. A reactorsystem according to claim 1, wherein the structured catalyst comprises afirst part arranged to generate a first heat flux and a second partarranged to generate a second heat flux, where the first heat flux islower than the second heat flux, and where the first part is upstreamthe second part.
 19. A reactor system according to claim 1, wherein saidreactor system further comprises a control system arranged to controlthe electrical power supply to ensure that the temperature of the gasexiting the pressure shell lies in a predetermined range and/or toensure that the conversion of hydrocarbons in the feed gas lies in apredetermined range and/or to ensure the dry mole concentration ofmethane lies in a predetermined range and/or to ensure the approach toequilibrium of the steam reforming reaction lies in a predeterminedrange.
 20. A reactor system according to claim 1, wherein the structuredcatalyst within said reactor system has a ratio between the areaequivalent diameter of a horizontal cross section through the structuredcatalyst and the height of the structured catalyst in the range from 0.1to 2.0.
 21. A reactor system according to claim 1, wherein the height ofthe reactor system is between 0.5 and 7 m.
 22. A process for carryingout steam reforming of a feed gas comprising hydrocarbons in a reactorsystem comprising a pressure shell housing a structured catalystarranged to catalyze steam reforming of a feed gas comprisinghydrocarbons, said structured catalyst comprising a macroscopicstructure of an electrically conductive material, said macroscopicstructure supporting a ceramic coating, where said ceramic coatingsupports a catalytically active material and wherein said reactor systemis provided with heat insulation between said structured catalyst andsaid pressure shell; said process comprising the following steps:pressurizing a feed gas comprising hydrocarbons to a pressure of atleast 5 bar, supplying said pressurized feed gas to said pressure shellthrough an inlet positioned so that said feed gas enters said structuredcatalyst in a first end of said structured catalyst; allowing the feedgas to undergo steam reforming reaction over the structured catalyst andoutletting a product gas from said pressure shell, wherein said productgas exits said structured catalyst from a second end of said structuredcatalyst; supplying electrical power via electrical conductorsconnecting an electrical power supply placed outside said pressure shellto said structured catalyst, allowing an electrical current to runthrough said macroscopic structure, thereby heating at least part of thestructured catalyst to a temperature of at least 500° C., wherein saidat least two conductors are connected to the structured catalyst at aposition on the structured catalyst closer to said first end of saidstructured catalyst than to said second end of said structured catalyst,and wherein the structured catalyst is constructed to direct anelectrical current to run from one conductor substantially to the secondend of the structured catalyst and return to a second of said at leasttwo conductors.
 23. A process according to claim 22, further comprisingthe step of pressurizing the feed gas upstream the pressure shell to apressure of between 5 and 30 bar.
 24. A process according to claim 22,further comprising the step of pressurizing said feed gas upstream saidpressure shell to a pressure of between 30 and 200 bar.
 25. A processaccording to claim 22, wherein the temperature of the feed gas let intothe reactor system is between 200° C. and 700° C.
 26. A processaccording to claim 22, wherein the macroscopic structure is heated sothat the maximum temperature of the macroscopic structure lies between500° C. and 1300° C.
 27. A process according to claim 22, furthercomprising the step of inletting a cooling gas through an inlet throughthe pressure shell close to or in combination with at least one fittingin order to allow a cooling gas to flow over, around, close to, orinside at least one conductor within said pressure shell.
 28. A processaccording to claim 22, wherein the space velocity evaluated as flow ofgas relative to the geometric surface area of the structured catalyst isbetween 0.6 and 60 Nm³/m³/h or between 700 Nm³/m³/h and 70000 Nm³/m³/hwhen evaluated as flow of gas relative to the occupied volume of thestructured catalyst.